|
By 58meteorranchero - 4 Years Ago
|
A bit of a long winded post. Guys I am having issues with my 4bbl carburetor that I installed last winter. I have a 272 that is 30 thou over and the late ford replacement heads so compression is on the lower end along with a stock cam. I put a 57 B type intake on the engine this last spring and have fought with it ever since.
So the carburetor is a 390 cfm 4160 that was 2nd hand and I rebuilt it. The rebuild included new throttle shaft bushings to make sure it was good and tight.
I have put on the quick change vacuum housing and have tried every spring tension. I have changed the vacuum housing from the 390 cfm without the check ball to one from a 600 cfm carb with the check ball to see if it helps and tried all springs. I have tried all pump cams and even put on a 50cc housing and tried all the cams including the brown and yellow ones. I have tried squirters all the way from stock which is 24 I believe up to 40.
I have made sure the arm is set so it squirts as soon as you get movement as there is not any slack. I have verified the float levels and have even tried raising and lowering them above recommended settings. I checked vacuum advance and distributor advance and timing is at 10 degrees initial. Vacuum at idle is 19" at 3000' in park and 15-16 in gear, it is a FOM, idle speed is 650 out of gear and 500 in gear. During my trials I discovered my fuel pump was weak so I changed it and it starts perfectly now, but I still have an issue.
The issue is that when I do anything other than a creeping acceleration I get a bog that can stall the motor AFM shows lean and it always lets me know when the secondary's kick in when cruising and give it more gas. If I step on it it seems to go fine. Is there any ideas you guys have? I am wondering if the carburetor is too small and the secondary's are coming in too quick? I am at my wits end and want to figure this out over the winter.
|
|
By charliemccraney - 4 Years Ago
|
First, take the carburetor back to Holley's baseline specs for that exact carburetor and start over. You don't need a 50 cc accelerator pump so put that away and don't consider using it again.
Make changes according to the AFM. If it shows lean, then correct that. A lean primary circuit can cause a problem like you are experiencing. Make one change at a time and write down changes in a notebook, in the order that they are performed. This way, if there is no improvement or something gets worse, you can more easily go back to something that was known to be better.
|
|
By miker - 4 Years Ago
|
I had a very similar situation with a 4160 in the 70’s. Started and ran, huge bog when you started out. Brand new carb in box. I took the speed shop guy for a ride, he sent me home to pull it and bring it back. 10 jet sizes smaller than spec on the primaries. Problem solved.
Like Charlie said, go look up the base spec, and take it back to there. You didn’t note the primary jet sizes when you rebuilt it by chance?
|
|
By paul2748 - 4 Years Ago
|
What distributor - didn't see it mentioned ?
|
|
By Ted - 4 Years Ago
|
Have you tried raising the float level? Also keep in mind that the secondary side of the carburetor has a ‘fixed’ idle circle and if it’s not working, then the primary side idle circuit will be running lean. Something else to consider is warpage at the throttle plate to the main body. How responsive are the idle mixture screws when setting the fuel mixture at idle? If unresponsive or not very sensitive, then look for a leak at the aforementioned throttle plate to main body gasket or an internal problem with the carburetor circuits. Don’t rule out the valve lash adjustments either. Does not sound electrical but if a points distributor, make sure the grounds are good and that the condenser is tight within the distributor.
|
|
By 58meteorranchero - 4 Years Ago
|
You bet I have gone from base line to settings to all the above changes and back. It is very frustrating.
Thanks
|
|
By 58meteorranchero - 4 Years Ago
|
All the jets pumps/ cams/ squirter was at the holley spec when rebuilt. This is what is frustrating every thing I have tried has been to cure that lean bog when transitioning from a gentle acceleration.
When I have a AFM on it my idle is able to vary from 11-14.6 with the screws. At cruise steady state I am a 14 when I step on it a bit it goes to 20+ then returns after the lag to 13 on good acceleration.
The distributor is the 1957 ford ball bearing breaker plate model and the vacuum advance is in good shape and will pull in a additional 15 degree of advance at full vacuum.
I have dual 2 1/4" exhaust on the vehicle.
|
|
By 58meteorranchero - 4 Years Ago
|
|
Valve lash is in spec and I tried opening it up to see if I had a sticking valve/ poor adjustment.
|
|
By 58meteorranchero - 4 Years Ago
|
Float levels have been also take from stock setting to way high to just below stock to try to see if it helps.
|
|
By 58meteorranchero - 4 Years Ago
|
|
Yes it is a point distributor and I have checked grounds. I also used a hand vacuum pump at idle to see if movement of the breaker plate caused the miss.
|
|
By Tedster - 4 Years Ago
|
The carburetor isn't "too small" you can rule that out, at least for the issue described. It should work well. For steady flat ground cruise I jetted the stock 2100 to run in the high 15s for AFR, with a good hot spark and plenty of vacuum advance this is optimal for clean burning plugs and at least a nod towards reasonable economy. On heavy acceleration it drops to 12.5 which is plenty rich for acceleration.
19" of manifold vacuum at 3000' ASL is excellent, so a logical question would be what flavor power valve are you running?
A 7.5 or 6.5 would be suitable with the numbers you describe. It is important to note that while the main metering jets are not part of the power circuit as such, jet size most definitely affects the AFR that is seen on power acceleration. The power valve only affects when the extra fuel is added, not how much. The PVCRs or power valve channel restrictors determines this, they are more or less fixed jets. The usual tuning strategy or "fuel curving" is to determine jetting first. The old school way was simply to jet down till "lean surge" or misfire was encountered and then jet back up 2 jet sizes. Then it's a matter of making sure that the power circuit is plenty rich under load. The wide band O2 AFR gauges takes the "hair shirt" element out of this operation.
The "transition circuit" or T slot is part of the idle circuit or just off it. Although it's called the idle circuit it is in play up to around 35 or 40 mph, if the idle mixture screws are too rich it can lead to a not so intuitive condition where the idle RPM is too high thus exposing too much of the T-slot. A lot of city driving is at idle or just off idle, so it is important that the idle mixture setting is set closely. A "lean bog" or "rich bog" is sort of similar in effect, the latter will be accompanied by a puff of smoke out the back.
|
|
By Cliff - 4 Years Ago
|
|
You may have a problem in the metering block (emulsion tubes), it's easier to try a different metering block than to repair it, however there are 2 small pressed in cups that have to be removed, drill a small hole in them insert a metal screw (not to far) and pull it out, you then can see inside and try cleaning, when done solder the hole in the cup and press it back in.
|
|
By Hoosier Hurricane - 4 Years Ago
|
|
You have 21/4" pipes on it. Do you still have the flapper valve on one exhaust outlet? Have you blocked the heat crossover in the intake? In my opinion you need that exhaust heat in the manifold to prevent a stumble on take off. On the race track you don't want or need that heat.
|
|
By 58meteorranchero - 4 Years Ago
|
|
Now that is a thought. I have the truck intake gaskets with the restrictor and no heat flapper on the exhaust pipe. It does have a bit more of a issue when cold, but even on a hot day fully warm it still stumbles.
|
|
By Ted - 4 Years Ago
|
Have you tried increasing the primary jet sizes? You don’t mention what fuel you are running but ethanol laden fuels do make the engine run leaner. And the 87-89 octane fuels have more ethanol content than the 91-93 ethanol laden gasoline. It would be easy enough to just increase the primary jetting 3-4 numbers and see if that either resolves or at least diminishes your hesitation issue. If you are running 87-89 octane gasoline, you can try the premium grade to see if that helps to alleviate the problem. If in doubt about the ethanol content in the gasoline, it’s a relatively easy check. The testers for that can either be purchased or home made as no special chemicals are needed for the test, just plain water.
|
|
By 58meteorranchero - 4 Years Ago
|
|
I run 91 octane premium in all my classics. This is the only gas up here that is supposed to be ethanol free as our 87 is E85 and our E89 midgrade is of course a blend of premium and E85. I have tried going one jet size up from stock setting and all I saw was cruise AFR go more rich. I have also tried a power valve change to a 9.5 just to see as my cruise is 13+. I think you might have hit on one of my issues when you mentioned the heat riser as when I built the car I gutted the old one and used it as a spacer. I just assumed the cold blooded nature was natural. I am not ruling out my metering block either. Has anyone played with the quick fuel universal metering block and any thoughts on whether it would work on a little 390 cfm carburetor?
|
|
By charliemccraney - 4 Years Ago
|
If you suspect that the carb is too cold and it has a spacer, try a spacer of a different material and possibly a thinner one. I dirve mine year round, even when below freezing, without the heat riser and restricted gaskets and the only time I had a significant problem was with a B-intake , 1" aluminum spacer and Edelbrock carburetor. The problem seemed to be carb icing, which occurred only below 40 degrees or so. The engine would eventually stall and after a few minutes of sitting with heat soaking into the carb, it would start effortlessly and be fine from then on. A change to a 3/8" thick gasket from Edelbrock took care of that and I didn't have the problem after that change. Note that there was never a problem when above about 40 degrees.
|