Hi everybody, this might turn out like a stupid issue in the end, but im stuck on it from a while. I have a 2.0 ford banger w/ 4 carbs, snowmobile/bike style mikuni VM 38s. Picture added, its from set-up day, now everything its tied up properly.kinda... Anyway, ihad many issues until i managed to make it a driver again, but then im stock. The mixture seems to be always rich, no matter whati do its alway pumpin some degree of white smoke and smells like unburnt fuel, im consuming the screws and screwdriver but w/ no avail. So i thought i could have too big mains, as previous owner had a ported head,theyre 250, so i ordered 180 and 200 mains (didnt get'em yet) but then discovered that 250 supposedly are the stock VM 38 main jets, and also that VM 28 moped carbs start from 160 till 200 mains, so if you add that up 250 dont seem too big for a 38 right? I mean if 200 its ok for a shitty moped engine on a 28 carb, a 250 in a 38 for a 2.0 litre engine should be small....or its this kind of reasonin total Bull? Anyway, symptoms:when i push the throttle down i can hear the fuel flushing in the cyl.s, literally, it makes a "fsshhhhhhh-ing" noise while accelerating but doesnt traslate to as much power, to be honest its worse that the previous single 2 barrel i had, so i know somthings wrong, and the smell of fresh gas makes me go the flooding cyl. way. Then consumption its total BS, i used to do 10 to 12 Km x liter and now im doin 3 to 6 if i go really slow, which is hard anyway, i moved the pressure regulator from 4 and 1/2 (recommended set) to 1 and 1/2, consumption got a lot better almost like b4 the carb swap but still i hear the flushing fuel and the smell of gas....and the total power loss just like b4.Im proly just saving fuel, period. Which its already a goal considering its 1.3 euros a liter Any thoughts about this? For those who might say check the head gasket and oil or water in the block/cylinders ive already checkt and block is sealed and rings are thight, so it has to be a fuelin problem, im also a little out of phase but i doubt this is the main cause and ill correct it as soon as i hook a phase gun on the block. Pls help, its my daily and only car at the moment, as my other truck might have a cracked head! tuff luck ah?
Well I don't know if this will help you any but on my Honda 250 the main jet is a 122. I was told that it was to lean because of EPA regs and should go up to a 125. it was so rich it barely ran. Intake design and exaust flow will effect what jet you will need. Mikuni prints a good booklet on the basics of jetting. Good luck with your problem.
Unfortunately you are right that your figuring on jet sizes is bull, There is no direct correlation between jet size and engine displacement. Bike engines have typically much higher CFM for the same displacement, and are jetted accordingly, to feed a car motor the jet sizes would need to come down some unless you use carbs off a relatively small bike, 38mm is not small for a bike.
Thanx coupster, this raises a new question? you say a 3unit increase made it waaaay too rich right? So theres not real need for me to go down 50 units i suppose, but then again i never heard a carb flushing fuel into the cylinders!!!! Of course im no pro, so it might be caused by somethingelse i ignore. As for the jet sizes idea i had being bull thanx for clarifing it, at least i know what not to consider!
this may help. I have done some setup work on sidedraft weber carbs on a Quad4 engine. What I found was I had to increase the size of the chokes( venturis) to stop that overrich problem. If that is a built motor you maybe pulling more air thru the carb then you realize. I am in the process of set up a 2.3 ford with alum. head and 45 DCOES and I am using 38 mm choke. Send me a note if you need more. mike
We ran a similiar system on a Ford 2.0 race car many years ago. As I recall, it ran pretty well from about 5,000~8,000 RPM. Never could get it to run decent below 4K. As we were fairly successful in class, the rules kept changing. Over about 7~8 years we ran several different carburetor(s). In order of best performance 1 - Carter 9400s (400 CFM) AFB 2 - Autolite 2100 (from about a 1963 Ford) 3 - the four Mikuni setup 4 - Weber 48 IDA The Carter produced by far the widest power range than anything. It also had better power, although the 2100 came close on power at WOT. The Mikunis ran well at high RPM. The Weber, well, lets just say I wouldn't do it again, knowing what I now know. Jon.
You have to really understand the way the bike carbs work to get them running right. The jet size question is directly related to displacement AND RPM. Bikes turn 10k to 14k rpm. You are turning maybe 6k at max? You can't just cut the jet size in half. A 100 main jet doesn't flow 50% of a 200 jet. You do need to start jetting it down, but there is a proper procedure to do this. Because the needles controlling mid-range drop into the main jet, you must check the mixture at wide open throttle. You didn't say if these are mechanical or CV (vacuume) carbs. This will make a big difference. If mechanical, you need only make sure your throttle pedal pulls the slides fully open. If CV, there is more to it. The throttle cable only operates the blades in the venturi. If the engine vacuume and the slide springs are not playing well together, you may not get full throttle with the butterflies wide open, or you might get the slides full open while the butterflies are at 50%. Either one will kill power and fuel delivery. I would map this with a digital camera taking pics inside the venturi at 25%, 50%, 75% and 100% throttle positions to see where the slides are at each step. Once confirmed to be reasonably close, you can go on to main jet size. Nothing else matters until the mains are correct, so leave the screws alone, leave the needles alone, just keep it idling. To set the main jet, you need a place (or dyno) to make full throttle runs under normal loads in an upper gear. Clean your plugs (new ones), Run it into 3rd or 4th gear quickly and hammer the gas to keep it loaded for 15 to 20 seconds, then cut the engine and go to neutral at the same time. Coast off the road, pull all the plugs and check the color. (I bet you have an idea of the safety issues at play here) Get this right before you do anything else. Once the mains are set, you can work with the needles. This will be about throttle tip in driveability. In a power gear again, 3rd usually, roll into the throttle and see what it does. If you are way off,it will be hard to tell rich from lean. Watch for fuel smoke out the pipe, listen to the engine tone and expirament. You can add fat needles to lean it out, thin ones or shims to lift them sooner to richen it up. When you have the throttle response under power reasonably crisp, you can then make final adjustments to the idle mixture. Now you can turn the screws. Idle it down as low as it will go and sync the carbs with mercury sticks. Then set the idle mixture by setting lowest stable idle and then adjusting mix for fastest idle. Reduce idle again and repeat. Blip the throttle to about 2k rpm. If it returns to idle gradually, you are still rich. If it drops below the idle rpm ad then climbs back up, you are lean. When it snaps up and right back to idle rpm, you are dead on. There are things you can do to CV carbs to make the slide springs open at the right speed by shimming the springs and drilling the vacuume orifice in the bottom of the slides, but that can get tricky. You need to get everything else very close before you go there. Good luck.
Well, what to say, thank ryan for keepin the hamb in life! and all you guys w/ all this info makin it alive! So, 1st thing 1st, where the heck did my engine picture go????? I see a lot of way off topic pictures lately that i very much doubt that a 2.0 liter pinto w/ four vintage carbs in a 70 model year ford got deleted right? maybe not, but still seems quite strange, after all this about an engine not about the car. carbking: either carter and autolite are just abount inpossible to find here and im already having big issues findin someone in knowledge w/ mikunis...got my point? Then i was thinkin, if you had this set up on a ford you should be able to give me a good tip on set up i suppose. its a stock 2.0 liters pinto, i just added the carbs w/ the intake and am plannin on gettin cam n skimmed head, but now its stock. scottybaccus: the carbs are VM round slide snowmobile type, it used to be a kit from esslinger engineering sold specifically for 2.0 ford 4 from the 70s till late 80s if i recall right.i've already contacted them as it seemed the easiest route but they dont seem to want to reply....go figure.. Then, ive already said im no pro, im kinda learnin while i go, but ive torn these things apart n i didnt see any butterflies inside????? what did you mean by "you may not get full throttle with the butterflies wide open, or you might get the slides full open while the butterflies are at 50%"? I totally understand the issues, safety and legal related, to testin the car on the road, infact that would be pretty hard to do here wheree i live. That said, how do i set lowest stable idle and then adjust mix for fastest idle? theres only one setting i can go w/ on each carb.....i have a feeling as this being a really silly question. Other simptoms are, depending on the idle adjustment i do: engine revvin to 4-5k in about no time and gettin down to 1k very slowly but then idleing kinda spot on, then by closing a bit the air screws engine still revs high very very quick but also go down fast, ifact that sounded spot on, if it wasnt for the fssshhhhhhing noise and the fact that after 1 minute driving it all got back to crap! i sync-ed the carbs w/ a tool i made myself w/ clear tubing and 2 stroke oil many times gettin them spot on at idle, but then when irev up every one "vacumed" diffrently, thats cause the 4 throttle cable retainers are screwed and they all pull diffrently, i probably managed to get all four slides to open togheter now, but still engine is clearly underpowered and gets too much fuel. Now its a few days that i just drive it as it is cause im moving to a new house and have also a truck that i need that might have serious trouble...anyway, engine also overheats, it might just be that i removed the heating conduits, and the route the water take s its shorter than b4, but still it seems too hot compared to how it was w/ the 2 barrel. What else can i say???? i cant put an air filter on cause i have the brake booster covering carb nr 4 and i should use individual filters, but then 3 filters and 1 w/out wouldnt be a good idea i suppose....this to say that air screw is very sensible...but dont think dis is much of an issue right? ....i must stop now im gettin headache! Thanx to all, ill check back laTER.
typically 109 CFM, so four of them is 436 CFM enough to run a small block ! I have a bank of 28mm flat slides on one of my trikes, each is supplying 425cc of car cylinder in mild tune, and runs good on the stock Mikuni jetting for a 250 motorcycle. Motorcycle carbs tend to be fuel pressure sensitive, often worth fitting a good regulator.
Thunderace,thanx, im assuming the jets were changed as the PO had a pretty souped up motor (cant get a hold of him either), in fact id like to know what bikes had these 38s and how they where ran, but i think they only were used on snowmobiles, and that kinda hard info to come by it seems. As for the regulator i have a mr. gasket one, ive seen it pretty often in many set ups, im also sure theres better quality around. Still by lowering its setting from 4 and 1/2 which was recommended by the tek sheet for this application, to 1 and 1/2 i inproved the fuel consuption issue from 4 km x liter to about 10, but still im running like crap, if only i had my truck runnin i would try harder!
Bonez - just read your location as being in Italy; so of course you are correct in that Carter and Autolite would be very difficult to find in your location, plus you would need to locate an intake manifold. As to giving you a tip on setup; we ran ours maybe 15~20 years ago. And I enjoyed them so much then I vowed never to touch another one, and I haven't! I really don't remember what our final setup was; but we could never get the engine to pull well below 4000 RPM, and not at all below 2500 RPM. Part of this was probably the fact this was a race engine, with a pretty wild camshaft. On WOT, they ran well enough that we won our division; thus being successful enough that the next year the rules were changed to "any single carburetor". The next year we went to the Carter AFB (and again won our division, getting the rules changed to "any 2 barrel"). The following year we then tried the Weber, and ran consistantly 5th the first few races until we switched to the Autolite. We then ran number 1 again, and again won. After a few years, they changed the rules to any carburetor as long as its a Holley 4412 and we quit! I am now going to bow out of this thread; and suggest you read scottybacus' posts. They look good to me. Good luck with your project. Jon.
Thanx carbking, i smiled readin at your last post, i think i uderstand your grief!, only in a very small scale...you must have had quite a nice youth mate, youre one of the lucky ones of the golden (or silver ) age of racing. Scottybaccus, carbking's right, your posts and the last specifically are very good, probably being real simply explained but accurate none the less. By readin one of your answers i think i found out what im doin wrong, and feel way too stupid to say what it is. Tomorrow or in the next few days i'll check it out, if im right im probably gonna solve the biggest issues....i guess ill let ya know as soon as i do it. Meanwhile thanx so much for your time and precious help!!! bonez
are the carbs off a bike? if so then there gravity feed, i would try a fuel tank hung just above the carbs. also what does your intake look like?, one carb per cylinder? then the carbs would have to be sincronised.
alright then, i looked at the exploded view an other material i have and made my mind up about what you (scottybaccus) said last night. I've attached a picture, hopeing this one will not be removed... of exaactley the same carb i have, except for the fancy billet-style trumpet, or velocity stack as u wish. i added sum numbers and reference to explain what i suspect. So: 1- main idle screw or tickover screw, is what the mikuni exploded view and online catalog call it. 2- pilot air screw its all there is to say about this one. 3- cable retainer its what is refferd as pretty much everywhere, but here is where i got illuminated....being used to a weber 2 barrel w/ just 2 screws, idle and air i never thought that the retainer could be considered as some tipe of idle regulator, even when i started messin w/ it tring to synch the carbs and noticed a change in idle revs. Is this the slow idle you refferring to yesterday, while tickover (main idle) is mid range regulation one? I suppose this could explain a lot of issues, proly not all of'em but pretty much solve the main problems, as i was tunin only main idle and pilot air,leaving the other pretty much unchanged. The only problem i see here would be the locknut inside the top of the carb cap, the one that keeps the cable retainer nut from gettin loose. The problem would be settin it and then unscrew the cap w/out losing the settings, w/out the bottom locknut would be pretty hard and inaccurate to say the least i suspect. Am i startin to get to the right path here? As for Budds question, yes kinda, theyre snowmobile kind and yes born to be gravity fed, thats way the "kit" came w/ a pressure regulator, suggested to be set at 4 to 5 (psi i suppose), but that because of the really over the top consumption i did set to 1 and a 1/2. Didnt change performance at all but at least consumption got down noticeably. Still way underpowered....and spittin unburnt fuel from the exhaust, sometimes if i step hard on the throttle at low gears and push too much fuel in, my eyes burn so much its difficult to keep'em open, and believe me that aint nice at 60 in traffic.. Then of course intakes are real short tubes, one x cylinder, just like this one, same thing, only diff. colors, also have the scoops, not that i can use'em, but i have'em and i sync-ed them many times but seems little to no improvement, but this might just got solved w/ the above discovery, just said might......dont wanna jinx my self...damn murphys law! Thanx all ya guys, get back year after i check this out for real. One last thing to scotty about the home made air box w/ one filter, thats my plan, only i need to take the brake booster out to get accurate measurements and i need to have the car off the road so that i can work w/out the hurry of gettin it all back 2gether by the mornin to get to work, so until my truck its fixed, none o'that gonna happen, and it might be very long as if it has a cracked head i just dont have the funds to buy the new one/ones.....life's a bitch! bonez.
I don't know of any bike that ran this size as stock, but certainly Mikuni sold 38mm round slides as upgrades for hardleys, and there should be plenty of test reports arround on that. The snowmobile being 2 stroke has a slight mods to the carb compaired to 4 stroke, but they can still work for you. As I said before you are way over carbed here, a 2 litre ford only needs about 200 cfm, even allowing for some improvements in gas flow, at full bore the carbs will still be at less than half the designed metering air flow, at part throttle things will be worse. Hence at best the results are likely to be as Carbking described. I would be tempted to reduce the number of carbs, and get a better match on CFM.
Interesting stuff. I'll just add that it seems today's gasoline here in the US doesn't color plugs as fast as the gasoline from the good ol daze. A few years back when little brother ran gasoline Olds' in his drag race Henry J it took a couple of 1/4 mile runs to get the color to show.
'Ace, thanx for the lead on harleys, ill be glad to check that out, as for the overcarbed theory im not really sure. One of the most common upgrades on pintos are the double IDF or DCOE 40 to 48 Webers, or DRLA still 40 to 48 and other equivalents from Dell'Ortos, even Mikuni had a double barrel carb in the same style and sizes as Weber and Dell (or maybe it was the other way around?), only i dont remember the name now, they were fitted on early 70s skylines, 240z and all those mini jap rockets w/ either L6 or 4 engines......and the Weber double double barrel mod is still goin strong in the old skool euro ford scene, so i suppose it has to be ok for the small 2 liters, for what info i gathered this is because the pinto block has huge intake ports, theyre like 50 or more,above other things, and a bigger carb should only improve things instead of making them worse... This set up im "wearing" was sold as an alternative to the above brands by Esslinger Engineering from mid or late 70s till maybe the early 90s, in case you dont know them, Esslinger Eng. is a Ford 4 only, specialist and a seriously good one at that, they used to be into racing big time, i dont know now, but if you go to their website this kit is still in their catalogues even if they dont sell'em nor produce'em anymore, the intake was cast by their shop, and the kit as a whole was developed specifically for the 2.0 liter pinto, that is why im pretty sure that w/ some patience, research, trial and error this can be made to run right. Unfortunately Esslinger it self doesnt reply to my questions on this specific matter, and the guy who sold me this its not much help, i mean, its a really nice guy, he used to have this on a 2.0 liter w/ cam and ported head on a 27-ish T cdan , but the only thing that managed to tell me was that the carbs were ready to be ran, just needed to set up idle w/ a unisync n i was good to go! He was so nice to send me the unysinc via usps, unfortunately it got lost in the bloody mail and never arrived.....sigh sigh, of course it wasnt as easy as he said, proly as my engine its a stocker while his wasnt. This issue about the ported head and race cam makes me go toward your overcarbed theory, but other than this im confident that ill make it go......eventually!, after all on the original catalogue it doesnt say that the engine has to be souped up, it actually says if i remember right something like "adds some go, or adds some power". Thanx, Nick.
An old carb tuner on a shop near where i live (that refused to help me cause he says its too darn time consuming) infact told me that to do this right i'd need some good old red gas!Was it called red in the States too? In my opinion this statement must have some degree of fact, but i suppose its overall Bull! C9, on the other hand i suppose every body here agrees that other than not being as good as the real thing the new so called "green" gas its full of dirt and if you run on a almost empty tank as a habit you risk to end up w/ a blocked off pump or/and carb, oh yes and filter!!! guess how i know!
Agree DCOE however if two fitted recommended choke size 32mm, ie might be a 40 or 45 body but metering is done by a 32mm sized hole, For nearer stock tune one DCOE with 34mm chokes would be the choice, ie even two 38mm Mukinis are 'more carb' than one DCOE twin choke !
if your carbs were gravity feed then they would have different needles and seats then ones designed to use a fuel pump, snowmobiles or any engines that have fuel pumps use a needles and seats with a smaller opening then carbs that are gravity feed, i have converted bike carbs to run on a smowmobile and had to buy the correct needles and seats, so an easy test is to use a small tank and gravity feed them, you can gravity feed fuel pump carbs at anything below WOT as thats when they would starve for fuel, so you didnt say if your intake has a common plenum, if there is no conection between the carbs then they should be sincroed useing mercury sticks, how about a picture of your setup?
I believe Budd is correct on the needle and seat info above. I do not believe the fast idle screw is what we were looking for. I expect that will be the enrichment for the chock setting, see the passage leading to the choke enrichment plunger? The actual idle, is the base setting, or preload on the slide lift. This is don individually on the cable, but collectively on four carbs, at the point where all 4 cables come together. This is a real pain in the ass on these type of carbs. I do want to say, these are newer than any I've ever worked with, and it has been a while. You should jump over to the Jockey Journal to confirm what I am saying. I would be able to see for myself if I had one in hand, but my memory and pictures are all we have at present. I see the fast idle screw as tuning choke enrichment, the pilot air screw as tuning idle mixture off the choke circuit and the cable setting the closed position of the slide for idle speed.
Right then, the .pdf file ive attached is page n 16 of the esslinger catalog, although they dont sell this anymore from a long time its still online. As its written, carbs come pre-jetted and modifiend, i suppose that takes care of the needle and seat doubt. Then this here is the link to the VM manual ive used to try understand how the darn things work while i took em apart, its been of some help, but not being an expert some parts are still not really clear to me, as you can guess http://www.mikuni.com/pdf/vmmanual.pdf This is my engine bay, still not real tidy, but then still not at 100%, ill take care of that once im satisfied w/ the performance. I hope this time around the picture doesnt disappear.......
are these carbs smooth bores? i was thinking of putting my 33 mm smooth bores on my 2.3, i ran my 33's on a 900 honda dirt drag/hill climb bike for awhile, converted them to run on alcohol for a time, hours and hours jetting them up to run right, now there back to gas and sitting in a box waiting, maybe its time to get them out. i have a new merc stick setup waiting it's trun as well.
Wow!! This one was unespected! Panic, as ive been sayin b4 today im movin to a new home and at the mo' im just here at my old apartment picking up some more stuff, so im not capable of giving ya all o'that info. Still, ill do a list between tomorrow and monday and see what comes outta it. Just a couple of quick ones: the head gasket is solid, theres no leaking nor any tipe of water loss from the rad., and the white-ish smoke now after eons of tuning is real real thin and for what i know was a consequence of runnin rich...but then.... Thinkin about it theres no way i could hear gas flushing into the cyl.s but i sure hear fuel flushing fast! It makes that noise instead of the "growl" that should make. Gettin back to 4-5 psi b4 i solve the problem would mean 2 to 5 miles x liter, and its just above my pockets Of course theres no "stock jets", what i should have said is those that came in the original esslinger kit One last thing, i might be wrong on one thing (actually i know im wrong in more than 1), whhen i said too big mains i meant the main jets, which in my head are those that are plugged by the needle, if im correct i didnt know i only need them from 3/4 throttle up. Well, thanx to all again, and panic thanx for taking the time and being so clear about everything, im sure nobody will get annoyed, after all you guys are all trying to help. Talk to ya guys soon, Nick.
Hey! what the hell happened to Panic's posts on this thread?? I was gonna write down the list he posted for me and here i am discovering that its disappeared?!?!?!?!?!?!
I ran a pair of those on my flat tracker Yamaha. The needle and seat is an issue, the pressurized one is different. Also float hieght and pilot jet size can be manipulated. They my be in sync at idle, but unless those cables are perfectly adjusted to where you hear one solid "thwack" closing, you have a problem with one or two being on a different circuit. The pilot jet is very sensitive on these carbs, if you have a lagger or two it will run pig rich. Make sure first they all have the same pilot jet, that is a common mistake. I bought a mismatched pair of 38 VMs and put them together and chased my tail until I matched the pilot jets, Just a thought. And they plug up too, which is just like having too small of one, and a clean that when synched will be too big. So, I would pull the pilot jets, make sure they are all the same and clean them really well and try again. Thest amount of dirt in any of the passeges really screws them up Make sure the slides are all perfectly opening and closing, when they are right you'll hear one tight solid smack when you let the throttle loose from WOT. Otherwise the carbs are all acting in a different position and might get on the main quicker or slower, a good way to burn a piston if one lags much because the timing will be there but the fuel wont. The slide lift is controlled by the cable adjustment, and they do change the idle, and when the pilot jet comes into play and they need to be spot on. If they have sat any time at all even over the winter on a bike pull them and clean the pilot jets those holes are so small, and they don't clear out runnning fuel through them. When I rode a bike even with CVs it was a yearly ritual.
On overcarburation, remember that it is an IR system, a vey short one too. I ran two 38 VMs on 45 cubic inches and it pulled like a freight train from 3000-8000 rpms. Balance and tuning will get you there.
The Jalopy Journal
