Stumped about 1100 backfiring

[Matt_E]

I've got this 96 Venture with an 1100 here that keeps backfiring through the exhaust and the intake.
Flywheel looks fine, as does the woodruff key.
Reeds are good.
Over the course of several hours of troubleshooting, it has gotten worse.
Grounds are all good.

The only thing I can think of is the CDI.
Does anyone have any ideas? :dunno:

 

[waterfreak]

how about the carbs? a lean condition will cause backfiring

 

[jkirkland]

How about the firing order? Maybe the leads to the coils got switched in the ebox? I bought a raider a while ago that wasnt getting spark on one cylinder and found one of the wires going to the coil in the ebox got dissconnected. Just a thought, I know the triples arent like the duals when it comes to which coil fires each cylinder. Good luck --Jason--

 

[Cannibal]

Partially clogged water box/broken baffles? Air sucking in through fuel selector? Fuel filter? Engine air tight? Check timing with light? Maybe the stator came loose and timing is way off?

Not that I know what I'm talking about, jJust throwing some things out there.

 

[Matt_E]

Carbs have been gone through and are fine.
Firing order has been checked and is fine.
Stator cannot come lose and screw up timing on this engine.

 

[2XLR8]

A loose wiring to or a bad pickup could cause this. This unit uses three pickups as it is old school. There is a good chance it is the cdi. If you can try to isolate the cylinder that is causing the problem by grounding the plug wire. If you find out it is one in particular cylinder check that lead to the pickup with an ohm meter as you wiggle the wires for a loose connection. The common ground connection from the cdi in the electrical box has to be good tight. I have seen backfiring due to that as well as a loose pickup at the stater.
Once you fix the problem check the fuel pump check valves because I have seen them get damaged from the backfiring. I use earplugs when an intermittent backfire is a problem. I hate these.

 

[Matt_E]

Will do, thanks for the suggestions.
It backfires randomly on all three cylinders, it's not just one.

 

[TOBY]

Have you tried unpluging the black/white side of the start-stop switch, and will it start or just crank than BANG? like its only gittin spark when you let off start button?

 

[tofa]

Hi Matt
I had a GP1200 that did the same thing and found it to be a leaking rear crank seal...I changed out the crank seals and its gone fine since.

 

[Matt_E]

Crank seals are fine.
Results do not change with stop switch unplugged.

 

[waterfreak]

I would say CDI for sure on this one. You should find a few of them for sale on pwcyesterday.com

and definetly check your fuel pump for those blown out check valves.

 

[Matt_E]

Easy enough to check on this setup.
I'll go over the grounds inside the ebox again while I take the CDI out.

 

[crashski]

could be your stator is bad, sounds like what mine was doing when i though my MSD went out.

 

[Matt_E]

It's not a typical SJ stator. The ignition is digital and uses individual pickups.

 

[Matt_E]

I pulled the flywheel cover once again and did a quick & rough indexing. #2 and #3 are roughly 1/3 of a rotation (120 degrees) apart, but #1 and #2 are about 60 degrees apart (1/6 rotation).

I daresay I have found the problem.

 

[Cannibal]

So it was a timing issue.....one crank throw was out of time with the rest....should be a pretty easy fix. Just fill that cyl full of water and turn the engine over 60*. Done :moon:

 

[Matt_E]

Because it twisted between #1 and #2, both #2 and #3 are out of time.

 

[OCD Solutions]

That's a good one to put in the old memory bank. Great troubleshooting Matt!

 

[Matt_E]

Unbelievable. I had never seen a twisted crank before. And as of tonight, I have two in a row.
A guy brought over a Polaris triple to have me replace a bendix. He just told me it needed to be replaced. His "other" mechanic had already taken off the flywheel cover. The old bendix had some teeth chewed up.
Okay, so I put a replacement bendix in it and it cranked fine.
Then I put some gas in it and tried starting it. It immediately backfired, reversed the engine and sheared the flywheel key.
So I called the guy up and told him about it. At that point he tells me that the engine suddenly stopped last time he had it out and would not restart. His buddy mechanic tried starting it several times before the bendix went out.
With this new information (I really wish people would tell me the whole story to begin with), I started thinking......it stopped, and when restarting was attempted, a bendix got chewed up.
I got it to crank fine as long as it wasn't actually firing. As soon as it fired, it kicked the engine hard enough to immediately break the woodruff key. :thinking:
So I indexed the crank. Wouldn't you know it, slightly out of phase.
I figure it slipped to where timing was over-advanced. When it fired, it kicked the engine into reverse.
The owner won't like that one.

 

[Cannibal]

Having been a car mechanic from 97-07, I am very weary of customers that (in my case) bring me a car, say "here, just do a 'tune up' on her". Then they come back and complain that the hesitation is still here and expect me to fix it for free. I never diagnosed a hesitation, you never told me there was a hesitation, therefore, we are back to square one.

My first question when someone tells me they need a 'tune up' is "WHY?". If the answer is, "she just turned over 90k and it's due", ok, sounds good. Usually there's another reason behind it though.