engine backfire and loss of power

[RAT]

My pickup spent 8hrs on the dyno trying to jet an Edelbrock carb. We gave up on that piece of junk and went to a Holley.

I feel yer pain. Not a fan of Edelbrock carbs. Ran a Predator 1250 on a 351 cleveland in pro gas eliminator class (not sure what class that is these days, maybe pro comp) NHRA. Loved that carb set up; it made massive amounts of HP. In a '72 Vega it was a blast.

[Roger]

You guys sure it's not a timing problem?

[RAT]

You guys sure it's not a timing problem?

If it was timing the engine would run rough at all altitudes. What he describes is that it runs ok at "home" but gets rough going up the hill.

[neilbyrd]

Well I jetted from 57 to 55 and now the soot is dry instead of wet. I had ordered 54 also so I guess I will try those next. I will need to get new plugs to because they are fowled now it wont run to much soot. I might order some 53 and 52 just in case.

[RAT]

Well I jetted from 57 to 55 and now the soot is dry instead of wet. I had ordered 54 also so I guess I will try those next. I will need to get new plugs to because they are fowled now it wont run to much soot. I might order some 53 and 52 just in case.

Yup! Sounds like you're getting there fast. One more jet change and you should be pretty close. How far did you drive it before you pulled the plugs?

[Jeeperator]

Hopefully he changed the plugs same time he changed the jets so he dont get a false reading from the previouse jet usage. Need to drive up a long steep grade in a higher gear 1:1 and at the top pull over fast and check the plugs. Driving around town is not goin to give you a good reading. Engine needs to be under a good load like it was on a dyno pull.

[RAT]

Hopefully he changed the plugs same time he changed the jets so he dont get a false reading from the previouse jet usage. Need to drive up a long steep grade in a higher gear 1:1 and at the top pull over fast and check the plugs. Driving around town is not goin to give you a good reading. Engine needs to be under a good load like it was on a dyno pull.

Yes, agree 100%.

[neilbyrd]

I drove up bee canyon to the big flat area above the shooting area and back to my house before checking them (about 10 miles). By the time I got back to my house it was barely running, thats when I pulled the plugs and saw all the dry soot. I will change the plugs and drop the jets 2 more sizes when I get them and give another go either saturday or sunday.

[Jeeperator]

Make sure your floats are adjusted right also.

[Russ Chung]

Make sure your floats are adjusted right also.

Good point. We know that the engine is running too rich. It might be caused by improper jetting, but it could also be caused by improper fuel level in the bowl if the float level is out of adjustment or the float valve is not closing tightly because of wear or age. I'm not familiar with the Avenger carb. Is there an external adjustment for the float level or do you have to take the carb apart to adjust it? Also check the float itself to make sure that there are no holes in it caused by corrosion. I would think that if the problem is due to the float level, the problem would occur at low and high altitude, but maybe it is running rich at low altitude but not enough to cause misfiring until you get to high altitude. But as Kurt said in an earlier post, just do one change at a time, whether it is the float, the jets, or different spark plugs.

[neilbyrd]

Last time I checked the float level it was at the bottom of the sight plug and the carb is only a coulpe years old and has external adjustments for the floats. As much trouble as this has been I am almost thinking I should just get a np435 and swap in the 318 mpi I have sitting around here.

[chris142]

Ya check the float level. I've seen all kinds of stuff get stuck in the needle and seats.
Pieces of rubber hose is the most common.

[neilbyrd]

Well I checked the float today and as soon as I pulled the sight plug gas poured out, so I put the clear plugs in and adjusted the level to just under the glass. I checked the seat and it was clean. the secondary level was ok. I put new plugs in it and left the jets alone for now. I will take it up the canyon a bit tomarrow and see what the plugs look like after that. Then I will see if I need to jet smaller.

[RAT]

You're getting a lot of advice here and that is a good thing. I just want to remind you to make one change at a time, and it helps to write down each change as you make it so if you need to go back you know where to go. I learned that from past experience in drag racing. Lists are a good thing...

[neilbyrd]

Yes I have been taking baby steps. I fix computer controled machines for a living so I know how important it is to move one thing at a time. Yes, I have gotten alot of good information from all of you guys and I want to thank all of you for that. In the morning I will be taking it out to the canyon again and see if it all pays off. Hopefully the improper fuel bowl level was the last problem causing the richness.