So I purchased a refurbished 600cfm Holley Carb straight from the source,I put it on in early January, and have been driving it occasionally here and there, and after got everything adjusted and while driving the car at even throttle i feel a consistent slight surge, I have checked and checked for vacuum leaks, at low and high rpm and found none. And now when I pulled in last night the RPM went from 600/615 to about 1500 in gear, and about 2000 in park.. I hopped out looked to see if something was hanging up like throttle plates on the gasket, or throttle lever hitting air cleaner. I backed out adjusting screw all the way, tried to pull back on throttle lever, adjusted the accelerator pump arm to where I had .010 gap, started it up and it was still sky high., so I pushed it in and called it a day. Called Holley, and they said well you only have a 30 day warrenty on a refurb'd one.. FYI keep that in mind if you happen to buy one from them, put it on immediatly, dont wait a few months like me.. They are insisting I have a vacuum leak. Here is what I have 1969 SBC 350/300 factory aluminum intake, Assault Racing HEI distributor, Holley 600 cfm 4 barrel, new fuel tank, new stainless, lines to new Carter mechanical fuel pump, metal fram inline fuel filter. Timing is set at 12 degrees before at 725/730 rpm, holding about 17 on the vacuum gauge. When put in gear it drops to about 15 which with what Holley says divide that in half and that gives you the correct power valve with would be a 7.5, from the factory it has a 6.5 but they where not 100% certain if that would cause the surge issue. But now that the high RPM issue is happening I am puzzled as to what that can be now. I can deal with the small surge issue after i figure out what can be causing a high stuck RPM. I haven't checked my fuel pressure yet, maybe I need a regulator but I have never needed one in the past with a mechanical pump.. Am I missing something.. I have all unused V-ports plugged, and all the other ports hooked up according to Holleys instructions., I have used brake clean, and carb cleaner on all possible areas where it could be leaking and have found nothing! So I am wodering what I am missing and if any of you guys have any ideas, or have encountered any of this or can shed some light or point out my ignorance on something obvious I am missing.. Thanks for letting me bitch, rant cry, compalin or whatever you guys think i am doing here.
Please be careful spraying brake clean anywhere it can be cumbusted , it generates deadly gas when heated . It could be deadly to anyone in your house if workin on the car in house garage or basement . Ok with that out of the way. Is choke flap wide open ? If so check to determine high idle cam is not holding a high idle . If it is not , I suspect warped throttle plate and or blown power valve . Either way sounds like you need another carb
Are you sure that the throttle plates are closing? Also, are the secondary plates closed as they should be at this point? It does sound like a vacuum leak, but it sounds like you've checked all the 'normal' places where you'd get a leak. The 7.5 versus 6.5 power valve would not cause this issue - so you either have a vacuum leak, or your throttle plates are not closing (my best guess).
So I have a few questions One make sure the throttle linkage has enough free play,the way I do that is to take the linkage off the carb and with the idle screw backed all the way out there should be a 1/16 to an 1/8"of free play to hook it up if not adjust it. The surge could be a lean mixture or a float that's out of adjustment causing bad fuel delivery. I like the front float just below the site hole and the rear just dripping out of the hole. And you didn't mention vacuum advance if you have one are you plumbed into the proper port,it should not be in a manifold vacuum port. I hope that helps Sent from my iPad using The H.A.M.B. mobile app
Ok thanks for the tip on the brake clean, will keep that in mind. I plan on checking the throttle plates in the AM. I was so pissed yesterday I just put it to bed and had a beer. lol The choke plate is wide open, I diconnected the 12 volt supply because I wanted to eliminate anything and everything I could think of that might cause the surge issue. The High RPM thing just started after about 10 minutes of driving after installing new fuel pump, which has me wondering if the pressure from pump is to high so that was my next diagnosis before I move on I guess.
Check and see if secondaries are rocking up and down on secondary throttle shaft set screw. It's located and accessed from underside of base plate left rear corner when facing front of carb.
I have had the carb on and driven with it for a bit but have been trying to figure out the surge problem since say early January, and the linkage and such has worked flawless. But after fine tuning it I still had a small tiny surge and then like I was saying I installed the fuel pump yesterday, and then after maybe 10/15 min thats when the high idle started, thats why I dont think its a clearance issue, because the carb has not been removed or nothing in the area has changed. I will recheck the float bowls, as I have them adjusted to where they both just start to trickle out. And I have the air fuel mixture adjusted to where I was holding the most vacuum (18)and turned them back to where the gauge was holding steady at (17) at normal opperating temp
I had a high rpm when warmed up/hot, acted like it was sticking . I tried lots of things , but finally installed new base gasket and tightened the mounting nuts just enough to seal. They evidently warped the base just enough to bind the throttle shafts. Edelbrock carb though
Well after pulling intake, replacing gaskets, inspecting carb inside and out, I found nothing visible that would have caused anything. the linkage moved free and clear, everything functioned as it should, did a compression and a leak down thinking I might have had a valve issue, and the compression was 175/177 across the board and everything was right where it was supposed to be as far as I could tell so I was really getting more and more puzzled. I even went as far as testing resistance on the plug wires, still nothing, so I figured, well maybe its something else so I figured time to put the plugs back in and as I was reading them and double checking gap i came across a plug that I must have either banged it when putting it in the first time, or dropped it and didnt recheck the cap before putting it in the first time,because the ground was almost touching the center electrode..Well lets just say I feel like a complete idiot, as I have burned up all my life lines, removed, and reinstalled the intake and carb 3 times looking for leaks, called Holley who insisted it was a leak, i was about to pull the trans thinking it was something going on with it possible. and all it turned out to be was a stupid error on my part. But I am man enough to admit when I make a mistake, and I have always said I am no mechanition. I figured I would post a update and admit my ignorance because I did learn way more about carb set up, carb function,timing, tunning and ignition set up than I ever thought possible, and maybe just maybe it will help someone who might be in my similar position.. So like they say, your never to old to learn something, always , ALWAYS double check your work, always be thankful to those willing to help and offer SMART advice, dont get in a rush, and ALWAYS DOUBLE CHECK YOUR WORK! thanks guys for all the tips and hints, they didnt go un-noticed or un appriciated.
Hmmm??? I can see where a bad plug can cause misfire issues, but not a high idle speed problem . . . that doesn't make any sense to me at all. If anything, you'd have had one less cylinder firing - that won't make the car idle higher. So - maybe you were fighting multiple problems - one related to a vacuum leak (which you may have fixed with all your gasket changes) and the other related to a plug. One thing to think about - if I ever "drop a plug" onto a hard surface - I go get another one to replace it. You can cause cracks in the insulator and easily not see them.
YOU ARE CORRECT SIR! hah I should have put that the high idle issue popped up and was the result of a vacuum leak on my part after my 2nd intake install trying to reuse gaskets while looking for the surging problem. And after i put new gaskets on the surging issue was still there, and thats when I started thinking it was a valve issue. Sorry for not being clear on that in the beginning. Im not a mechanician, or a technical writer.. haha
Good point on the crack plugged also. I am not 100 percent that it was dropped or what exactly happened. there where a couple different hands involved at various periods during all this, so its hard to tell what exactly happened, just glad I found out it was a plug way before I started loosing whats left of my mind!
Thanks for posting the update, wish more would man up like you did. The rest of us learn from the many knowledgeable people here but as you saw many times doing a long distance diagnosis is an educated guess at best, and a wag at worst.
I never claim to know it all or even a 1/4 of it.. Yhea long distance diagnosis is always a crap shoot but I only hope that maybe I am over looking something obvious.. In this case not only me but my buddy was also puzzled by it and then even more elated when we found the plug that wasnt gapped and caused the surge. Hell who am I, I am just a guy who likes to mess with cars, and hopes that he can take them out and beat them only to do it again.. We only learn from failure right?
The Jalopy Journal
