3.0 engine lean, backfire please help

[cbucner]

I adjusted the idle screw as instructed by DonS but still that won't solve my problem.
I can't get it over 3000 rpm not even , at about 2500 the engine starts to loose power and backfire.I just can't figure this one out.
I made a video so you guys can see what's going on.
Here's the link to it.
Clink on it and then open.It's about 10mb.

http://64.65.22.75/filme/engine.wmv

Please watch it and tell me what's next??
I'm going crazy with this boat.
Thanks for any replies.

 

[b0mbtrack]

Re: 3.0 engine lean, backfire please help

is it hitting on all cylinders?

 

[cbucner]

Re: 3.0 engine lean, backfire please help

The engine runs fine at idle and up to 2000 rpm.
I'm thinking it's the carb or I don't know.
I have new wires/spark plugs/distributor cap.
All new fuel filters too.
Thanks

 

[b0mbtrack]

Re: 3.0 engine lean, backfire please help

see if it is starving for fuel when you get up there on rpms. to do that try to close the choke with something long like a stick incase it backfires. do that while someone else drives. if the rpms go up when you close the choke you know it is a fuel problem. or if you can, look into the carb to see if the secondaries are openning up or not. or try to spray some fuel into the carb to see if it picks up rpms.

 

[cbucner]

Re: 3.0 engine lean, backfire please help

I squirted some gas in the carb and the engine picked up rpm but still was not running quite well.
I think it's an electric problem.
My alternator was down , was not charging , not it looks like it's charging again so I think there an electrical problem that throws my ignition bad.
The alternator was showing 10-11v an the gauge with the engine running, now it shows 14-15 again so I don't get it what's going on??
It showed 10-11 when I started up then after a while went to 14-15v .
It bugs me so bad.
Thanks

 

[cbucner]

Re: 3.0 engine lean, backfire please help

I will wait to see what DonS has to say.
Thanks

 

[freddyray21]

Re: 3.0 engine lean, backfire please help

the alternator should put out about 14-18 volts when charging. If you shot gas to it and it picked up I don't think it's a spark problem. I think Don would say: When was the last time you changed your water/fuel seperator? Is the fuel pump weak? . I think you need to look at a fuel issue.

 

[Silvertip]

Re: 3.0 engine lean, backfire please help

If the electrical system is not charging, or charging intermittently, low battery voltage would certainly cause a high rpm miss which is evident by the engine shaking. Fix that problem first. Since you replaced the distributor cap, are you sure you have the plug wires in the correct firing order? Did this problem appear suddenly, or has it been gradually been getting worse. Have you checked ignition timing? Have you checked fuel pump pressure?

 

[cbucner]

Re: 3.0 engine lean, backfire please help

The fuel filters are all new from one end to the other one.
The only thing I did not check is the fuel pump pressure.
What's the normal rating for these fuel pumps??
And how can I check it.
I have a fuel pressure gauge but I need some fittings to fit it.
Any ideea where I can get them?
The alternator looked like it had a bad connection by the plug.
I sparyed some electrical spray and now it looks like it's charging 14-15v.
I took the carb apart today and cleaned it , used some air to blow all the holes made sure everything was clean and free of debris.
put new gaskets and put it back.
Now runs little better , it goea to about 4000 rpm but then again when it gets there starts to lack power and the rpms goes down if you try to push it or it will backfire.
now what??

 

[cbucner]

Re: 3.0 engine lean, backfire please help

I checked the timing and it looks good.
In base mode 2deg after TDC and it advances to 25bef at 2500-2800 rpm.
It looks like it's running better now but still when you're tring to get it from idle to WOT somewhere at about 2500 has a hesitation and then it goes to WOT.
But that's on the muffs, I bet on the water I can pass that 2500rpm because it will start to hesitate and that's it.
I'll see what Don S will say.

 

[Silvertip]

Re: 3.0 engine lean, backfire please help

I have no idea what kind of fuel pressure gauge you have but whatever fittings you need to couple to the fuel line can be obtained at any auto store or in the plumbing section at any home improvement store. Disconnect the fuel line at the carb, slip a rubber hose over the end of the line and clamp it. You are looking at only 4 - 6 PSI from a mechanical fuel pump.

 

[cbucner]

Re: 3.0 engine lean, backfire please help

I looked at my fuel test gauge today and was perfect for the job.
Had the same 5/8 threads so it screwed perfect on the carb and the same with the gas line.
I ran the engine and the pump is pushing a steady 6PSI.No up or downs.
From what I learned today I think I figured this out .
When I first start the engine and it's cold , I'll let it warm up to about 130-140 then I took it from idle to 4400rpm runs like a champ.
Let it run for 5 mins it got to 175-190and stoped it.
Then after 10 min start it up again and it shakes at around 3-4k rpm and I can bet it's one of my ignition components that gives me the problem once it gets warm.
After all the trouble and everything I changed on this engine , the only thing tat it can be is the ignition coil / advance chip or pick up coil.
I will look into that tomorrow.
Thanks guys

 

[Jack2]

Re: 3.0 engine lean, backfire please help

Hello,

Have you solved the problem above? Now I have the same problem and can't figure out what's wrong. The engine takes about 2400rpm without any problems and then when I pull more rpm they starts to travel between 2000-3000rpm. The problem appeared suddenly after about 2 h boating.

 

[bruceb58]

Re: 3.0 engine lean, backfire please help

You should start a new thread instead of trying to revive this old one. You can also send the original poster a message. You will have a better chance of getting his attention.

 

[Haut Medoc]

Re: 3.0 engine lean, backfire please help

Hello,

Have you solved the problem above? Now I have the same problem and can't figure out what's wrong. The engine takes about 2400rpm without any problems and then when I pull more rpm they starts to travel between 2000-3000rpm. The problem appeared suddenly after about 2 h boating.

Welcome to iboats......
Have you changed your water separating fuel filter if you have one?....
Your problem could be water in your gas....
Start your own thread & tell us what year/model of your engine & describe your problem.....

 

[Wotam]

Re: 3.0 engine lean, backfire please help

"I'll let it warm up to about 130-140 then I took it from idle to 4400rpm runs like a champ."

Ok, so heat is affecting something to make it cut out. Coil? Change the Condenser? (if it has one). You could take it to a boat-friendly auto shop that has an engine 'analyzer' (ignition scope). Put your engine on the muffs, attach the scope leads and run it. If it's an ignition problem the analyzer will show you what's wrong very quickly. Probably the best $60 you could spend on this issue.

The other possible problem (shudder) is that the engine is getting water in the cylinders when it gets warm... a crack opening up, gasket failing, vacuum leak at temperature ?

Do you have access to an old fashioned intake vacuum gauge... they were an invaluable tool in the old days. (before computerized engines)

 

[Don S]

Re: 3.0 engine lean, backfire please help

Just another old post.​

Start a new thread Jack