Backfiring 717. Please help I’m loosing this battle

[smaguire93]

So I’ve got an arch nemesis and it’s a 2000 seadoo gti 717. It’s torturing me....

so the ski ran fine. But decided to change the fuel lines as green goo was starting.
So new fuel lines and carb clean. Didn’t remove anything else.

rebuild carbs twice (genuine mikuni kits) pop off pressure 22 and holds 10psi for ages. Followed rebuild treat to a tee both times.

now my issue is whenever I come off WOT and then slam accelerator again I get an almighty backfire each time.

Idles perfect. Can be hard to start. But once going starts easy.

so far I’ve rebuilt carbs twice,
New spark plugs,
Trimmed spark plug leads

I’ve tried running from a separate fuel line to exclude bubbles. Done the same thing.

tried it a few times with flame arrestor on and sent it flying through the air

I really just want to get this thing going

 

[mikidymac]

I would be looking at your accelerator pump. Is it squirting, did you replace the little hoses on it?

Do not run it with the airbox off as it will be too lean.

 

[smaguire93]

I would be looking at your accelerator pump. Is it squirting, did you replace the little hoses on it?

Do not run it with the airbox off as it will be too lean.

Great to hear from you again! Yes it’s pumping well sending a great little spurt every time I hit the accelerator. Going to put the air box back on now and try again.

 

[mikidymac]

Did you replace the little accelerator pump hoses?
Did you install new needle and seat?
Did you change the pop-off spring?

 

[smaguire93]

Did you replace the little accelerator pump hoses?

I managed to get them off cleaned and replace the vent on the originals

 

[mikidymac]

You have to make sure you still have the restrictor jet in the line feeding the pump as most people don't know it is in the hose and throw it away.

 

[smaguire93]

Yeah still in it. Seems to have a good flow

 

[smaguire93]

You have to make sure you still have the restrictor jet in the line feeding the pump as most people don't know it is in the hose and throw it away.

Could I have put the restrictor in backwards? Would it matter?

 

[mikidymac]

No, I don't think it matters as it's just a restrictor orifice.

 

[smaguire93]

So an update. Rebuilt the carbs again. Using all genuine parts (second pack now). Checked all fuel vent lines. Accelerator pump works well, put old pulse line back on.

so as it currently sits. It bogs down on acceleration. Takes some time to get up to fulls revs. Then when you floor it. Backfires like crazy. Any suggestions before I sell it as parts?

 

[mikidymac]

What is your battery voltage at idle and at 5,000 rpm?

The rectifiers can make crazy things happen when going bad. You might be moving on to electrical issues with the backfiring.

 

[smaguire93]

this has been at the back of my head as a potential cause... there’s no rpm gauge. I’ll try get some stats tomorrow for you. Any other tests which would be handy to do to have results for?

 

[etemplet]

So an update. Rebuilt the carbs again. Using all genuine parts (second pack now). Checked all fuel vent lines. Accelerator pump works well, put old pulse line back on.

so as it currently sits. It bogs down on acceleration. Takes some time to get up to fulls revs. Then when you floor it. Backfires like crazy. Any suggestions before I sell it as parts?

Stick with it. Frustration is normal. All that bogging and backfiring tell me the ski isn't getting the fuel it needs. I hate those carbs with the accelerator pump so much I often just buy new ones. Problem solved.

Did you look at your rotary valve plate? I'd check that out. I think you have a fuel issue more than electrical. If the internals of that carb are not clean you'll have problems and you'll keep having them. I ended up buy an ultrasonic cleaner to do my carbs. Cheaper method is to find a buddy with a good carb and stick it on there., or buy a new one. They run sweet with a new carb. Good Luck !!

 

[Mekanix]

A few things going on here.
You are hitting the rev limiter and backing off just as it does that
The low speed orifices are clogged partially or the pilot jet is still partially varnished. (still looks clear until you run a cleaning pick through it and clear varnish comes out.
Same issue with the main jet.
All circuits combine to give the full fuel flow. Those carbs are lean from the beginning. Anything that blocks the passages will cause this.
Best thing is to replace the carb.
otherwise it takes quite a bit of work to clean out a carb properly and get every passage clean as new.
Another option is to go up a few sizes on the pilot and main jet.

 

[smaguire93]

Hey guys. Thanks for all the reply’s. I really appreciate it. Especially the encouragement to stick at it. It’s such a love hate relationship. But it’s still fun tinkering with them. So I put the ski on the lake and it sounds a lot better.

A few things I noticed. When idling the ski drives around about 2mph so I think the idle screw is in too far. The backfiring is much less. I get 41mph but it doesn’t sound right. I think it’s pushing the engine too much. My plan is to decrease the idle and change the throttle position so WOT isn’t quite so high.

I’ll post a link to some YouTube videos. Apologise for the quality.

it takes some time to get fully going. And if you go from 0-WOT if dies down as if struggling for fuel. Then after a second it’s all systems go.

low speed adjuster is one turn out and high speed 0 as per specs.

any further adjustments to try tomorrow?

once again thank you all. Especially to mikidymac who has always be there to help.

 

[mikidymac]

I still say something is wrong with your carb and/or fuel system by the way it is running.

Idle should be about 1500 rpm in the water. Changing the idle will not change the wide open throttle opening and you should not be restricting wide open throttle.

Top speed should be about 45 mph.

What is your compression?

 

[Mekanix]

Well wow!!!
Your prop and wear ring are shot.


There is likely nothing wrong with it fuel wise but you are absolutely bouncing that thing off the rev limiter.

 

[mikidymac]

Well wow!!!
Your prop and wear ring are shot.


There is likely nothing wrong with it fuel wise but you are absolutely bouncing that thing off the rev limiter.

That would be an easy fix. I didn't watch the videos.

 

[Mekanix]

That would be an easy fix. I didn't watch the videos.

Oh yeah, like a Honda civic in 1st gear

 

[smaguire93]

It’s a brand new wear ring and prop was good. Some very very minor marks on it.

Oh yeah, like a Honda civic in 1st gear

Ohh the vtec!

 

[smaguire93]

So pardon my ignorance I’m very new at this. How do I stop it bouncing off the Rev limiter? And any ideas on the bogging down going from 0-WOT

 

[smaguire93]

I still say something is wrong with your carb and/or fuel system by the way it is running.

Idle should be about 1500 rpm in the water. Changing the idle will not change the wide open throttle opening and you should not be restricting wide open throttle.

Top speed should be about 45 mph.

What is your compression?

Yeah somethings still not correct. But it’s running?...ish.

I got a compression tester off the internet. It read 125 both cylinders. But I don’t trust it. It’s quite hard to get a compression tester here in Ireland. People keep laughing when I ask about them in auto part stores. They keep asking how old is my car!

 

[Mekanix]

I am not sure if I would trust that compression tester because that engine sounds very healthy. Normally when you're at wide open throttle, The engine goes all the way up to just before hitting that rev limiter. The only thing that prevents it from hitting the rev limiter is the load that the Impeller puts on the engine. If there is damage to the impeller or the plastic ring around it is damaged or there is too much of a gap around the impeller then what will happen is something called cavitation and that is what rhis sounds like. For that bog from idle to wide open That is going to be the low speed circuit. It's Is likely still partially clogged. Something that can help with this is to remove the pilot jet and spray carburetor cleaner through that passage with the low speed adjust all the way closed and do this for almost half a can of carburetor cleaner. Another way to
compensate for this is to go up 2 sizes on the pilot jet.

Even though excelerator pump is working that doesn't mean that there is enough fuel in there to begin with which is what the pilot circuit is for.

 

[smaguire93]

I am not sure if I would trust that compression tester because that engine sounds very healthy. Normally when you're at wide open throttle, The engine goes all the way up to just before hitting that rev limiter. The only thing that prevents it from hitting the rev limiter is the load that the Impeller puts on the engine. If there is damage to the impeller or the plastic ring around it is damaged or there is too much of a gap around the impeller then what will happen is something called cavitation and that is what rhis sounds like. For that bog from idle to wide open That is going to be the low speed circuit. It's Is likely still partially clogged. Something that can help with this is to remove the pilot jet and spray carburetor cleaner through that passage with the low speed adjust all the way closed and do this for almost half a can of carburetor cleaner. Another way to
compensate for this is to go up 2 sizes on the pilot jet.

Even though excelerator pump is working that doesn't mean that there is enough fuel in there to begin with which is what the pilot circuit is for.

Thanks for taking the time to explain it to me. Makes much more sense! This is my second gti of this age. I replaced the wear ring in both. This ones is brand new and a nice snug fit! Much snugger than my other one, impeller is also in better condition.

will try the carb cleaner tomorrow have been using compressed air and carb cleaner. Only in short blasts tho. Will try a good sustained clean!

 

[1of500]

Pull the pump and take some pictures of the pump and support plate shoe ect did you install the gasket with the pump?