QuestionQUESTION: HI Matt, I have a tuning problem I hope you can help me with. I have an SBF (302, .030 over w/ less than 5
miles on rebuild and professionally assembled short block, ported/polished,
headers, MSD 6A ignition box,Streetfire distributor, MSD cap and rotor, 8.5MM
MSD Wires, Accel 50K HEI coil, Edelbrock Performer Manifold w/650 elec. carb,
new everything under the hood, less than 5 miles on the rig)in a 1982 Ford
Bronco. Here is my issue. It idles alright (a bit "choppy"), but when I put it in gear (4 speed manual) and try to
accelerate it bogs down and stalls then has a rough time restarting. Basically
I have to floor the throttle to get it to start. When I give it some throttle
at idle it has a hard time smoothly advancing through the rpm's. I have found
no vac. leaks anywhere, I have good hot spark and plenty of fuel. I have
advanced and retarded the timing (rotated the dist. in both directions) with no
real improvement. I have also adjusted the fuel mixture on the front of the
carb in both lean and rich directions again with no significant improvement. I
am a little bit weary of my initial timing. I have never done it before so I
wonder if it is possible to be one tooth off in one direction or the other and
still idle fairly well. I hope this is enough background for you.
ANSWER: Hello Chris. This must be very frustrating for you having spent so much time , effort and cash on your car and it not be running properly.
Tricky question but I'll do my best and i have to be honest may take 2 or 3 e-mail to crack but don't worry we'll solve the problem !!
First of all although you say you have adjusted the ignition timing and you say its putting in the correct amount of fuel but i have to say that the most obvious thing i can think of is that the engine is running far too rich. You can simply check this by looking at the spark plugs after you have run the engine up (idle it from cold to hot and you will see by the colour of the plugs. If it revs ok at say 5000rpm after a few seconds of holding the throttle then this is because all the fuel and air are burning once you have settled with the throttle. Possible if it is having trouble accelerating to higher RPM it could be the accelerator jet/s in the carb could be blocked (im not to hot with carbs if im completely honest)
It could also be that the engine has not been dyno run and that the rings are not bedded in and there is alot of oil being burnt in the cylinders but this is less likely , you will see if this is the problem if there is lots of blue smoke coming from the exhaust when the engine is running.
So are the first things for you to do
1)Check the plugs after run up
2)Try lean off the mixture by adjusting the jets
3)Check there is no/not to much smoke coming from the exhaust when idling.
Your suggestion about being 'a tooth out' is possible but we will check the basics first.
get back to me soon as you can.
Matt
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QUESTION: Okay, thanks Matt, here is what I have so far. I pulled a plug (#5, easiest to get to) and it had a lot of black soot on it. I believe this is the result of a rich mixture. However, I have previously tuned the carb down low enough that the truck nearly dies and I still have the same issue while under acceleration. Should I crank the mixture screws down then alter the position of the idle screw??? I just thought of that...any other input you have would be great. Thanks again, I'll see what happens and get back to you. Thanks.
ANSWER: Absoloutly yes - crank down the mixture screws till it nearly dies (600rpm?) and the wind up the idle screw. The result of this being that you take out fuel and add more air. A very black sooty plug means too rich. However please bear in mind that this may not be the ultimate soloution and you could end up driving away with a mega lean engine which is very dangerous - always use high quality high octane fuels !!
Let me know how you get on....
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QUESTION: Okay Matt, I backed the fuel off and my truck still would not barely run when I tried to give it the "GO" juice. I checked for kinks in my fuel line, debris in any fuel lines and cleaned the carb (even though it's new). Where should I go next? My only two ideas are: 1)bogus timing and 2)I think I need high(er) octane fuel. What are your thoughts?
AnswerOk so we can pretty much say that its not a fuel issue if your still having the same problems but it may be something we'll come back to if we are still struggling.
Dont worry to much about the fuel for now but something around a 102 octane should be ok for when the thing is running properly.
So timing , you said previously that you have tried advancing and retarding the ignition with the distributor and it made no difference so its more likely to be the cam timing. Did the company who rebuilt the engine not dyno run or even fire it up ? Is it overhead camshafts or push rods ? A good check at this stage would be to do a leak down test to check that the valves are all closed when at TDC on each cylinder (remember that you could be 180 degrees out when doing a leak down test) Let me know if you need anymore 'talk through' advice on how to do this.
Matt
