Projects Shade tree Model A speedster kind of thing

I adjusted the valves again. I didn't do a good job the first time. I don't have a hand crank for this thing, and I don't think I was successfully getting all the way around to the heel of the cam on every valve without one. All but one of the gaps were off, all too wide. I made this thing this morning from an extension I ruined trying to get an O2 sensor out of a cursed non-Hamb mess we used to own. It is way too weak to start the car, but it will turn it with the plugs out.



It was sure worth the 30 minutes or so it took to slap that together. I also recommend taking the manifolds off, also worth the extra few minutes.

The jackleg crank made it much easier, and I'm confident the lash is right now. Here's a video of the idle:



I haven't road tested it yet, but I'm pretty happy so far. Knock on wood.

 

Very kool! I just love this thing!

 

My usual practice is to retorque the head, while it is still warm from running it in, and then reset the valves. To retourqe the head bolts, I was taught, and the usual practice at the heavy duty shop, was to loosed each bolt one at a time 1/4 turn loose, then back down to the correct torque, you'll often pick up a couple of degrees per bolt.

 

Happy New Year, everybody.
Blues,
I had already re-torqued the head, but thank you for the reminder, anyway. Didn't seem to pick up much if any rotation on any of the nuts, so I hope that's ok? Anyway, I started it back up after that for a road run, and it was running like crap. Here's why:



That's the intake manifold. Guess I tightened it a little too much when I put it back on from adjusting the valves the 2nd time. That ear must have popped off as it was cooling down from my second run- in. Dammit. I know that crack looks rusty and old in the picture, but it's just the lighting. Honesty compels me to report that the broken edges looked real fresh, no evidence of a previously existing crack or casting flaw. This one's on me.

Anyway, I wirebrushed it down and sanded the outside edges back and brazed it yesterday. Went back this morning had hit a couple of spots on the inside where I hadn't gotten a complete flow through, then faced it off and threw it back on there (carefully, you know), didn't even touch up the paint I had burned off, Y'all. I like the way the brazed repair kind of winks at you from the depths, even though it's not the prettiest job. I decided not to sand it down and pretty it up, but left it ugly for strength. It fits the rough and tumble nature of the car, anyway. Knock on wood, but it seems to be running well again. The low this morning was in the mid 30's here, and it's still in the mid 40's, so I'm going to wait until after lunch for a shakedown run. I'll do my best to post a video, if no new thing arises.

 

Just read the whole thread, amazing job and amazing car!

 

Good job on the brazed repair.

 

I am having a time with this thing. It runs fine in the yard, but when I get it on the road, it falls on it's face. Pulls hard halfway through the rpm range, then just stumbles and won't go. Skips, backfires through the exhaust, won't take gas. So, I have been using the old process of elimination.

First things first, used carb cleaner to check for vacuum leaks. Didn't find any. I remembered the old maxim that 90% of carb problems are ignition problems, so I looked there. Checked the timing, in case I accidentally put the distributor gear back in one tooth off, but it's good. Good strong spark at the cap and each plug, maybe the condenser can't keep up with higher rpms? It's the only old part of the system. I have a spare, but it didn't have the little bracket to screw to the distributor body, wouldn't make good ground, so I jacklegged it. That's it next to the original.



No change. I'll put the original back and keep old jack as my spare.

Next I checked the mixture on the SU. The car idles fine, but seems lean on the road, skips and backfires through the exhaust. I already had it set as rich as the adjustment would let me. That big nut varies the depth of the needle in the jet.



Remember, these carbs only have the one needle, which does everything. Screw it out, it pulls the body of the jet down, enriching the mixture. I turned this little doohickey from bronze to allow me a little more adjustment before I loose the spring tension.




That helped, but the problem isn't fixed. My thinking now is that maybe I do have a vacuum leak, but that it's small enough that it doesn't affect the idle, and doesn't show up with the carb cleaner trick, but it's letting air in at higher rpms? Doesn't really make sense to me, though. Isn't the vacuum highest at idle? Anyway, I ordered a new manifold gasket, just in case.

Before anybody suggests it, I'm sure I lined the cam and crank gears up correctly. The tooth with the dot on the cam gear is in the valley just to the right of the keyway. Anyway, it idles too good for the valves to be out of time, seems to me. I also changed my fuel filter, took the carb apart and cleaned out the jet and float needle to make sure it wasn't a fuel starvation thing. Compression is good, just under 80 for all four cylinders. I'm stumped.

My next step is to start adjusting that big needle in the SU to enrich the mixture off idle. I assume it's pretty common to have to adjust the carb jetting after installing a hotter cam? Any suggestions are welcome. Don't worry about insulting my intelligence. There are a lot of holes in my education, when it comes to this stuff.

 

Since I’m not an SU guy, do these have a choke or an enriched circuit? Maybe try enriching it while tooling down the road.

Another idea if that won’t work is another fuel source. When I worked at the dealership back in the good old carburetor days we used a setup that used a propane bottle for setting idle speeds and mixture screws along with searching for vacuum leaks under 440 intake manifolds.

Just a thought,
Cliff Ramsdell

 

I just read the thread through from the start, loving this build and the fettling process. I am doing exactly the same thing with a 1926 T that I bought as a rolling chassis some time ago. I have fitted a single 1.25" SU from a Morris Minor and am using modified model A manifolds. I live in Scotland so was brought up with SU's and have used them on all sorts of car and bike projects

I would hazard a guess that the higher lift cam is looking for more fuel than the carb can supply in the mid range and you will need to start carving the needle to suit again.

 

With the road performance ''falling on it's face'' and not wanting to insult you, have you got oil in the SU damping chamber?? (where the brass screw cap is on the top)
It controls the speed the piston and needle assembly, rises with the change of manifold vacuum..
Over time, I have used auto trans fluid, thru to 30 -40 engine oil, to get the right lift rate of the piston/needle assy..
Too thin oil, lift rate is too fast = rich mix.. Too thick oil = slow lift rate, lean mix..
Just a thought..

 

Thank you all. Like I said, I won't be insulted by any offers of help. Inthweedz, I have indeed checked the damper oil, which is 10w30 motor oil right now. I might try something thinner. Cliff, it has an enriching circuit, as opposed to a choking system, and it does respond to it on the road, but I have maxed out my mixture adjustment so far on the rich side that I don't have enough movement left to really cure it, which brings me to Blackbob's suggestion of thinning down the needle. That's kind of where my thinking is, too. I haven't ever "cammed" an engine up before, so I'm not familiar with how normal it is to have to adjust the carburetor jetting afterwards. This isn't supposed to be a real extreme grind, but I think it's maybe a little hotter than a stock Model B cam. Anyway, thinning the needle will be this weekend's project.

By the way, Blackbob, do you have a thread on your T? It sounds mighty interesting.

 

Oh yeah, Cliff, I'll try the propane trick. Good idea. Thank you.

 

Brazing is often underrated as a means to join metal, understanding you don't have a choice really with cast iron. Wish I could offer some ideas about your engine issue. Good luck.

 

From hazy memory you can somehow attach a wire to the piston and have it sticking up through the vent hole in the damper cap. You can then use it to tell you how far up the piston is, and hence which part of the needle is in use at that moment. You can then thin that part of the needle to richen it at that specific point. With an open engine car like that you should be able to see the carb from the drivers seat.

I suspect that the carb is not big enough. People used to use big 2" SUs. Not sure what they came on. Jags maybe?

Actually I'm pretty sure that carb will strangle that motor. You either need something a lot bigger or go to a more common setup like a 94 or 97.

Or how about a twin SU setup? A pair off a Jag should be plenty.

Mart.

 

Mart,
That's a possibility, but a Stromberg 97 flows around 150 cfm, and an SU HS6 flows around 200 (according to Google). This should be plenty of carb for my set up, if I can get the right needle profile. I think I need to just keep fiddling with it. I've said this before, and I could very well be wrong, but the engines that use 2 of these SU's, though admittedly half the size of mine, also rev twice as high and make twice the horsepower. Plus, it was running really well with the stock cam.

 

Something I should do, in the meantime here is a recent pic of it

 

That's just perfect. Thank you for showing it. I really like it.

 

Thank you still a lot to do but I am enjoying fettling it into shape.

 

10w 30 is way to heavy for damper oil. ATF is ok , 3 in 1 oil or various grades of fork oil. Also dont overfil the damper .It should not be filled to the top of the chamber just a little way down the tube attached to the piston.
The oil won't make it any richer or leaner , as the air is also metered at the same time as the fuel . When the piston /damper rises the venturi increases in size. So the the mixture is solely controlled by the diameter of the needle in the jet at any one time. Oil is only for damping , to stop the damper fluttering /chattering . The spring controls the rate at which the piston rises
Piston Springs
Paint colour on end of coil

Type
Load at Length Part Number
Light Blue A 2.5 oz 2.625" AUC 4587
Red A 4.5 oz 2.635" AUC 4387
Yellow A 8 oz 2.750" AUC 1167
Green A 12 oz 3.000" AUC 1170
Red B 4.5 oz 1.530" AUD 4355
Yellow B 8 oz 1.530" AUD 4398
Green B 12 oz 1.530" JZX 1088
Red & Green A 11.25 oz 3.875" AUC 4826
Light Blue & Black A 4.5 oz 3.875" AUC 2107
Light Blue & Red A 18 oz 3.875" AUC 4818



Spacing the jet down from it's seated position will increase fuel , but it will upset the float level and the fuel delivery if it is withdrawn that far .
The lowering/raising of the needle by the nut is a narrow range for idle mixture only and the manual lowering by the cold start enrichment (choke on other carbs) is also connected to the throttle plate for fast idle. and is only for that purpose.
If the jet is lowered the tip of the needle will possibly come right out of the jet and if it is low enough the fuel in the float chamber will be higher than the jet orifice so fuel will just pour into the carb and will not be controlled. It will also have a different fuel dispersion and therefore mixture if the fuel is being drawn across the mouth of the jet or the larger hole where the jet rides (i.e if the jet is withdrawn ).
You either need to change the needle or modify the needle or use a bigger jet. SU makes a .090 jet which I think you have and a larger 0.100 jet . You could try reaming (carefully) the one you have. That will increase fuel across the entire range of your needle.
Standard SU metering Needles are measured every tenth of an inch , (there is a list , but it is a book so a bit hard to repeat here ) so if you want to modify the needle , you need to assemble the carb, mark the needle where it meets the top of the jet at the top and bottom of the piston stroke then try and estimate where the needle needs modifying , remembering that the piston/needle will rise slightly at idle so the part of the needle metering at idle will be inside the jet when it is static.

 

Man, thank you for that post. I'll change the oil in the damper. I hadn't even thought of enlarging the jet. I'm tempted to try that, since my needle profile seemed to be working so well with the old camshaft. I have a spare jet from the partner of this carb, which has a busted housing (some previous owner dropped it on cocrete, I think), so I can always go back if I mess it up. I have a good, complete set of machinist drill bits. I'll try .098, then work my way up if needed. I haven't pulled the jet down far enough to get below the float level yet, so that's good, but the business about fuel dispersion makes sense. I should be able to eliminate that bronze spacer I made if I enlarge the jet. Now I'm really itching to get at it. Thank you again, 97.

 

Yes the twin HS4s have the 90 thou jet, the single most often have the 100 thou. The jet itself is only about 1/10th of an inch thick, the rest of the tube is quite fragile ( be careful how you hold it to enlarge the jet ) and is in fact only the jet holder, to put the jet in the correct place. I have been in the carb business for nearly 50 years, and I think SUs are probably my favourite carburettors. Not for any other reason than pure simplicity and versatility.

 

For some reason this thread & the Seagrave in Brazil are my fav's. I could NEVER do anything this cool.
Always look forward to this.....THANKS , rwrj !!!!!

 

Thank you both.

97, mine is an hs6, are the jet measurements the same?

 

The HS 6 will already have 100 thou jet, and a needle made to match, i.e they start off fatter at the top to control idle mixture. You could try enlarging it a bit, but be careful that you do not take it past the point where the needle can control idle mixture. Remember that small increases will make a way bigger difference to area as the hole gets bigger. I was going to mention that you may have idle issues if you used a modified 90 thou needle and a 100 thou jet, any bigger than a few thou over the 100 and it could also get dicey. You may have to stick to modifying the needle, or change to twin carbs. Preferably do not take any material off where the needle is in the jet at idle . i.e. the fattest part.
I had read all of your thread but forgotten the size of your carbs.
One thing you could try would be a stronger spring in the suction chamber, after you put the lighter oil in the damper... or if you still have the spare standard spring you could try stretching it a little at a time.... once stretched they won't go back.

Twin carbs will bring it's own issues with it. Not the least of which is your damaged carb....How bad is it?
New needles are available as are most parts for SUs. Even some HS8s used the 100 thou jet , although some of the later 2 " carbs went to a 125 jet , they had needles to match , which are also available , However I think you would be moving the air fuel ratio too far if you bored the jet to 125 . It is possible that it would work, but
Either an HS8 or a pair of the smaller carbs will probably be a better choice.
I have run a pair of HS8s and a pair of H6s on Model As and they worked without changing the Jaguar metering....it is a plan for my retirment years to do some experimenting there..( probably a lot of broken motors and parts...)

 

97,
That's good information. My second SU has a pretty seriously busted intake flange. I don't think its salvageable, at least not with my skill set. You've given me plenty to ponder, though, and I appreciate it. I hesitate to admit it to you, but my needle is already homemade, so no telling what kind of mess I've gotten myself into. It worked really well with the old cam, though, pulled hard all through the range, and didn't act lean (skip, backfire, run hot) or smut up the plugs any, so I smugly thought I had lucked out with it. I might just push that luck, chuck it back in the lathe, and sand it down an even thousandth or so, just for fun. I'll be careful with the big idle end, but it could stand a richer idle, too. I made it, using dial calipers, to a straight taper, so I'll just try to stick to that, or maybe a little more off of the middle than either end. I'll be sure to report back. I don't mind publicizing my fiddling around, even the failures, for the benefit of others. Haha.

 

Nothing to be concerned about, that is hot rodding, if it wasn't for hotrodders 90% of advances in engines and performance would never have happened.
If you cannot find new needles in the US , I will see if I have something here I can mail to you to play with.

 

Kevin Kay Restorations in Redding CA is a good source for S.U. parts here in the US.

 

Thank you both. I worked on it some yesterday, just chucked the whole piston in the lathe, colored the needle with a sharpie so I could have some indication of where I was taking material off.

I measured it with dial calipers at 1/4" intervals and went to work with 220 grit paper backed by a flat steel plate, then polished it up to 600 grit. I took about 0.005 off of the top, about 0.008 from the middle and maybe 0.01 at the tip. I'm now consistently about 0.006 smaller than the measurements of a stock KD HS6 needle, according to the internet. Lots of rain yesterday, but I was able to set the idle mixture, which is now right in the middle of the adjustment range without my little spacer, so I'm cautiously hopeful. I'll try to get a road test in this morning after the rain clears on out. I'll report back.

 

rwrj, make haste to git er back on the road.......i wanna go fer a ride in the woods....

 

Man, me too. The weather just won't cooperate today. The real rain has gone, but it's still drizzly and dark and wet, just not the weather for this car. Maybe later in the afternoon. In the meantime, I consoled myself by working on my gravity fed reserve fuel system. I found an old petcock the right size in the junkpile, and an even older 3/8" socket u-joint.



Did some drilling and cutting.



I rounded off that stub on the petcock where the handle was, dis-assembled the remaining part of the u-joint so I could drill a new hole 90 degrees to the stock one, drilled another hole through those ears and the handle stub, popped in some jackleg rivets, and got this:



It's not too pretty, but it will allow me to run a rod through the firewall so I can switch it from inside the car. I might just use a 24" extension and fab up a handle for the inside. Why complicate things?



The idea is, when I run out of gas in the main tank, I'll just reach behind me and pop the gas cap to release the pressure (it's possible without too much contortion), then switch to the reserve tank and poot on off. I'll loop the fuel line from the rear over the reserve tank, so I don't just gravity feed back into the main tank, then tee it in just past the petcock.