Hi guys. I'm here to ask what are possible causes for this stumbling or hesitation on acceleration. When I start to get on it, pressing the pedal nearly to the floor, i get this like chugging going on like its gonna die but at high rpm then all of a sudden it kicks in and I go flying down the road like I would expect, but initialy theres hesitation.
Please help me with possible causes
replaced plugs, plug wires, new electronic conversion.
Sounds like carb related, maybe the accelerator pump linkage has some free-play in it, or it might have a clogged passage. Make sure the gasket fully clears the pump discharge passage, even enlarge the hole in the gasket if you have to. (Assuming a Rochester Q-Jet.)
Hmmm.. Its an edelbrock , carter copy i think. 750cfm. I had a shop set the fuel mixture with a sensor and it had extreme hesitation, so obviously something wasnt right. I turned the screws out some to richen to the mixture and it seemed to get better but i'm having a hard time setting it to where i can withstand the shaking of a rough idle and alos eliminate hesitation.
I was curious if something else may have been causing it, the timing is set to 9 which is correct according to the books i've read.
How old is carb. With the car running put a rag over carb. If it stays running takes off thats a vacume leak. Or it may have picked up a piece of dirt to have carb rebuilt. Just .02
It's missing quite a bit when it gets warm.. at idle in park I cannot notice the misfire at all but when I put it in drive , and the idle is low it randomly misfires or starts bogging down, even died on me just now. My hesitation issue might be when it is missing because sometimes it just goes and other times it chugs, I might have to try another carb this weekend... The carb is pretty old, 7-10 years.
I'm not sure if this is the same issue or not but I have a new edelbrock 750 on my 400 and I have hesitation when starting from a complete stop. I have the jet kit for the carb and have installed nearly every combo in the book and can not get rid of the hesitation. I've tried adjusting the accelerator pump also. If I put my original Q-jet back on (which was rebuilt over 14 years ago) it runs fine - not quite as strong at high rmps but much smoother and no hesitation whatsoever. A friend of mine suggested that the 750 may be too big for my set up which is pretty much a stock rebuilt 400 with an HEI. If you find a solution, I'd love to hear about it.
Hi Davey, missed you when I was down, saw Robert from up in your neck of the woods...
Anyway, you say you think it's missing also? Then I would first check the plugs again. Check for wet or oil soaked ones and change again if needed.
Then yes, with the motor running, you can spray some WD-40 around the carb base lightly, and see if it picks up... if so you may have a vaccum leak which could cause some of the problem.
I would maybe contact Edelbrock, they are usually good with customer service, and have a tech dept. to help.
Then I'd try swapping the carb with a new base gasket etc... and see how it works...
I'll check all the plugs again... some of the old plugs had a slight bit of oil on the threads, not sure if thats normal or not... but on another note I just bought me a brand new holley 650 vacuum secondaries w/elec choke last night.. kind of excited about it...
that hesitation thing bothers me too much... on the holleys I have never seen that issue. When I pull up next to a chevy I want to show it who is boss.. ive already got a few mustangs stuck in my air cleaner...
1. Carb bowl level 2. Fuel filter(s) 3. Timing 4. Bad valve springs 5. one or more intake lifters collapsed 6. lobes on cam gone 7. plug wires routed incorrectly 8. Vacuum low.
You should have optimal 17" at the carb port. Lower for high duration cams. I run 5"
The Torker is WAY TOO MUCH for a 350 and those 47 heads. The intake, heads and carb is mismatched. The heads are 1.96/1.66 and will not breathe. The Torker is a high flow/high rpm intake which when you put 750 cfm carb in to a 950+ cfm intake to 650 cfm heads, you get the problems you convey.
What cam???
Without knowing how it ran before..what was done, if you ran it to 5k and dropped oil pressure. You may wish to reflect and post the full shebang.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
Hmmm. I don't know much about the internals of the engine or what might have been done to it or possibly wrong with it... this is how it came when i bought it. Maybe I should slap a stock 4 barrel intake on it??? we have a few laying around here.
I'm going to put on a holley 650cfm carb.. wonder what it will be like with that intake... There is a carb spacer on it too.. dont know why its there, but should I remove it as a temporary measure?
Thanks for the info... the car only misses when its fully warmed up... when its still cool it runs fine other than a idle that seems to get worse with each day. Timing set to 9 btdc Wires routed correctly Fuel filters new dont know about valve springs, lifters or cam.
Try running a blend of VP C-12 108 octane racing fuel with 93 oct. pump fuel. I run this in my '69 4.1L OHC6 250 Sprint, 10.5:1 comp. ratio, and it makes all the difference in the world. It woke this 6 banger up! Vp fuel is actually good for your engine..it's pure hydrocarbon fuel which tends to clean while producing a better burn giving you better response, no clatter or stumble. I usually mix it half and half, sometimes straight, when I can afford it. It runs about $4.35 per gallon. Check it out sometime!
Here's my two cents. A dual plane intake and a Rochester. I had a Holley 650 and a 750..niether performed as well as the Rochester once it was tweeked. I had a 66 mustang with the same hesitation problem...until it reached about 3000 rpm..then it would go like hell.
Tom brings up some good issues with the intake and missmatch. Try the new carb with one of the stock intakes, or better yet, try the existing carb on a stock intake, and see if that will make the difference?
Or if your just going to keep the new carb no matter what, go for that. Usually a spacer is a good thing, but in the right combination and application. So try that on the stock intake first if it fits, and then try it with out...
Try a few combinations to see what works best for your set up... If you keep the Holley, I might be interested in the old carb. Just looking for something cheap to toss on my truck to get it going.
Anyway, keep us posted, would like to hear the results! Thanks and good luck!
Cool cool.. i just remembered that i put some 89 octane in it last time.. maybe i shoulda put 91. I'm going to try the holley 650 with no carb spacer and leave the current intake on and see what happens. I'll let ya know about the carb Brett..... I just drove by the gas station.. 91 octane is 2.30 a gallon... man that sucks. At times like these i need a 4 cyl just to be able to afford gas!
Not all of it , there`s 3 grades there too, slightly higher octane than these here ,but still I think they go 92,95,98..?Forgot now , but when I lived there we had 100 oct. also...but then it was $1.00/gal and here .18/gal....its all relative ,but always higher there...and the gas there is the same price, its the tax thats *somewhat* different.. Bjorn
small 4 cyl`s , lika Alfa Romoeos, some Beemers , high hp Fiats , then of course Ferraris, Lamborghinis,Maseratis to mention a few...and It was more prominent use before of high octane gas for high compr. engines...the 67-69 Firebird orig. 400`s could use that... Bjorn
European engines are as small as 1.0 litre and top out at about 2.0, except for the really BIG engines like a 2.8 litre. (To compare this to cubic inches, a 1.0 l engine is 61 cubic inches. The 250 OHC six is a whopping 4.1 l!) They use very, very high compression to get enough power out of them. SAAB even has an engine where the head is on a rocker and can vary the compression ratio from low 8's to high 10's. That's some cool technology. They almost always have a much longer stroke than bore diameter. For these reasons they really need high octane. Unleaded gas was just becoming available in the early 90's...
OK ... somehow I don't think this is solving Davey's problem.
What's the latest Davey? Did you fill up with better gas, despite being gouged at the pump? Did you look for vacuum leaks? Did you swap manifolds? I do have an extra stock cast iron manifold with a July, 1969 date code - if you need one ...
LOL guys... no word yet, been a bit rainy here and not much time after work to get much work done on the car... i'm still waiting for the new holley carb to come in the mail... i'll try the carb first then start going from there...... you know I do not think I have a vacuum leak after close inspection, however I have a big exhaust leak and its blowin alot of air right out between the head and the exh. manifold... wonder if the exhaust leak has anything to do with it.. let me hear you guys's thoughts on my exhaust leak.
It was a small leak but recently has gotten to be a bigger leak.
Once the air is out of the cylinder, it won't have all that great an impact on the performance. A new gasket will make it quieter, which is the only contribution to a pleasent drive you'll get from it. (By the way, I'm not talking about a 600 HP racing motor that is sensitive to every little thing.)
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