1988 marathon No Start

LAZYK

I have a problem with our '88 marathon. The engine was rebuilt a year and half ago at a cart shop, new crank, connecting rod/piston. About a month ago it started acting up, drive it for 10 feet, 1000 feet, and it may not run again until it sat for a while. It seemed to occur more after making a tight turn. I changed the ignition system to a GM hei and coil and it ran better for a while but had a periodic backfire. Kept getting worse, will not run at all now. It has good compression at 120 psi. I have replaced the carburetor and fuel pump, new HEI module, reset the igniter coil air gap to .019, checked ignition timing marks alignment, and installed new crankshaft seals. So, good compression, strong blue spark, plenty of fuel from the output side of fuel pump, and suction at the throat of the carburetor.
Try to start it and one backfire out the exhaust and then nothing but turning over after that! I know little about two-stroke engines, but it seems all the elements to run are there: compression, air, fuel, and spark. What am I missing? Where do I go from here? Please help.

BGW

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cart around

How long ago was the new pump installed? It sounds like a ripped diaphragm to me.

What oil ratio are you mixing? I really hate to suggest clogged exhaust, but you are running out of options.

Could you list the things that were replaced before it quit running, and then a list of things replaced after it quit running? I'm trying to get a feel for the time line.

LAZYK

The pump was the last thing replaced, along with another front crankshaft seal, a back-fire blew out the new one shortly after replacing both seals. The pump will deliver 8 oz of fuel while cranking in approximately 15 seconds.

fuel-oil ratio=128-1

When running it would carbon up the spark plug. Not running-a no start spark plug-ends up wet--flooded even with healthy spark.

SEQUENCE OF EVENTS
Running poorly:
Good compression, 120psi.
Was fouling spark plugs so I cleaned carburetor, several attempts lowering the float level to prevent fouling of plugs, back to original float level.
Replaced stock ignition with an HEI and coil that I had laying around, along with a new steel core plug wire--ran better, but still had a miss.
Replaced HEI module with a new one, tested coil resistance, within specs. Tested igniter coil resistance, within specs, set air gap.
New Carburetor.
New Crankshaft seals.
At this point it seemed to run well for a ride up and down the driveway, then bam, back-fire and has not run since.
Replaced front crankshaft seal that got blown out, rear looks fine.
New fuel pump.
Put old carb back on just to see if it would make a difference--none.
Removed muffler to make sure there was no restriction.
Tried advancing and retarding the timing to see if that would make a difference. Nothing.

Today I am going to get some fresh fuel and a new bottle of synthetic 2-stroke oil, and try that. Don't know what else to do. What do you recommend for a gas mix ratio?
Thanks for any and all suggestions on how to proceed.

cart around

I'm at a loss. It appears that you have done everything right.

See what you think of this. http://www.ngk-sparkplugs.jp/english.../03/index.html

I say fouling is caused by too much gas, or not enough air. So where is the extra gas coming from?

Try running it without the air cleaner, and spray some ether on the rear seal.


The backfiring is definitely a problem. I wonder if the rear seal was damaged while the front seal was blown out.

I popped mine after a fresh rebuild too. Stuck it back in, and staked it the second time.

128:1 is a good mix.

Just had another thought. Pumping a lot of fuel is a good indicator that the seals are good.

I really don't know what else to tell you. That thing should be running.

LAZYK

Update: I had removed the duct from the air filter to the carburetor to eliminate any restriction. Today I emptied the gas tank, blew out the fuel lines, put the new carb back on, re-gapped the spark plug to .035 instead of .028 to overcome any ignition problem. New fuel and oil mix. Now it tries to run with some choke, but a lot of back fire out the exhaust. Improvement over nothing!!! The replacement carb has an adjustment on the air bleed. I set it at 1 turn out, is that OK?

I agree about pumping a lot of fuel, the rear seal looks good, but I am not familiar with these two stroke engines. Since it now is backfiring again, could it be a cracked piston or rings? Timing off? Advanced or retarded?

Like you said, this should be running, and I am running out of hair on the top of my head!!!

Thanks for your thoughts and continued insight.
Lou

cart around

The only thing I can say is that if the problem persists after changing parts, it's something that wasn't changed. You are running out of options.

Maybe torque on cylinder bolts.

Backfiring out the exhaust is incomplete combustion. Raw gas is getting into the exhaust.

I know that you changed the fuel pump, but this is really screaming ripped lower diaphragm.

Read this thread, and then take your old pump apart. http://www.buggiesgonewild.com/gas-e...fuel-pump.html

I have also attached the 85 manual. Yours is the same except for a different exhaust, and larger carburetor. Your choke plate will be vertical instead of horizontal. The section on carburetors is very thorough.

I can troubleshoot the 2 stroke 2 pg engine pretty good, but you have me stumped. There is something we are missing.

Attached Files

85-EZGO(2) (1).pdf (6.71 MB, 0 views)

Spicyunicorn

Is it pushing any fuel back into carb/intake?

LAZYK

Spicyunicorn: I have not noticed any push back into carb/intake, but will take a closer look.

Cartaround: In my travels through the forum looking for answers several weeks ago, I found the manual you had posted for others. I printed it out and have found it very useful. Thank you for your help, you have undoubtedly saved many a cart owner time, money and frustration.

Great pictures of the fuel pump showing what to look for. Today I will take the old pump apart and report back.

Thanks again,
Lou

LAZYK

Disassembled the old fuel pump today. Diaphragms intack!!! Will be gone to a car show for the next couple of days, but when I get back I will take apart the new fuel pump and check for a blown diaphragm. Thanks for the encouragement and advice. There is always a light bulb on moment, sometimes it just takes longer than others. Will get back to you all early next week. Need this thing running.

Spicyunicorn

Well I was going to suggest reed problem but if it's not puking fuel into the intake they are probably fine