carb backfiring

[lmtpop]

ok have performed the duraspark conversion on my BII, rebuilt carb (2150), now it fires, runs for about 10 sec's then flames out through the carb. i have reset and verifiyied the timing to be set initially at TDC a dozen times. the dizzy is turning. am now thinking it is the carb. any suggestions? additionally the originial dizzy cap had no. 1 to the left of the hold down strap the new dizzy cap has no. 1 to the right of the strap. all parts came from the dura spark recommended parts. it just seem odd.

 

[kimcrwbr1]

Its just out of time set it at 10 degrees with the pointer not the round thing with a light. If you ndont have a timing light stop and get one you will never get it right without a timing light.

 

[lmtpop]

will try that next. what is that round thing anyway? any idea why the dizzy cap is different between the original one and the duraspark one?

 

[PetesPonies]

THere is specific place the number one wire MUST be. It's all relative. If you have it pointing to number one when number one cylinder is on the compression stroke, you have it right. Then you have to wire the cap in the correct order and correct direction.

 

[cammeddrz]

pete is right, #1 is wherever the rotor is pointing when the #1 piston is in the correct firing position.

it really could be any one of the 6 posts on the cap, depending on where the rotor ended up when you dropped the distributor into the engine.

 

[PetesPonies]

and to add . . because of where advance mechanisms are located on the distributor and surrounding interference, there are "best" locations for the distributor to sit to have room for adjustments and such. But still, number one could be anywhere.

 

[lmtpop]

backfires only now a little

ok readjusted timing but now running about 27 deg btc. idle is high but if i retard timing it dies, will continue to adjust idle and timing. had to find my tach to determine what the idle speed is. any suggestion on carb adjustments?

 

[PetesPonies]

No way that engine needs 27 degrees BTC to keep running. Something is still amiss.

 

[lmtpop]

fast idle too much advance

yes i will be working on getting fuel/carb idle balanced with timing in the next day or so. air/idle mixture screws are a 2.5 turns out. what jets size should i run, the carb is off my early bronco 302 i just borrowed it figuring that one is a much longer project. could jet size be an issue?

 

[PetesPonies]

Jets are not operating at idle or low speed. Its all done from the idle circuit and transition circuit.

 

[lmtpop]

where do i hook up the vacuum advance to any port on the carb or intake tree?

 

[PetesPonies]

Well thats a big can of worms I don't want to confuse you with. So being PC, I will say to the carb.

 

[kimcrwbr1]

You want the advance running off ported vacuum on the carb. At an idle there should be no vacuum until you open the throttle. Try turning the idle air out 1 1/2 turns preset and what kind of spacer do you have under the carb. For the motorcraft/autolite 2150 you need felpro #60529 spacer to plug the big vacuum leak where the old TPS sensor was. The spacer is for a 302 so it should work just fine for the holly carb. It comes with gaskets on both sides but you will need to make one for between the carb and spacer. Do not overtighten the carb down pull it down slow until its good and snug after a couple complete warm up cycles give it another pull when cold.

 

[kimcrwbr1]

To surface the base of the carb I glue a sheet of 200 grit to a good flat piece of plywood and carefully surface the base until it all shines the same usually the ears just need to be knocked down a bit.

 

[PetesPonies]

I personally run all my vehicles, that have vacuum advance ,off of manifold vacuum. I want the advance at cruise, when my foot is out of it. It help MPGs greatly. YOu can tune for it. However, as I said before, don't want to confuse you when you are having hard enough time getting your engine to run correctly.