Problem starting engine after carb rebuild

[TXSpeedster]

Hello all,

I rebuilt the carbs on my right engine and now I cannot get that engine to start and run reliably.

The right engine on my 98 Speedster has always been a pain to start. When cold it starts eventually after many attempts and throttle juggling. When warm it still takes multiple attempts but does start a bit easier.

Thinking it would solve the problem I decided to rebuild the carbs (remove dirt, etc) but since I completed the rebuild and put the carbs back on the engine I have had the following issues:

1. Have been able to start on trailer but engine will die when throttle advanced quickly.
2. When it does start in water which is rarely, will only start with full throttle and will only run with full choke.
3. Sometimes it will start running in water without choke but with heavy vibration which I am assuming means running on only one cylinder.

It seems fuel supply related but I am not sure what to do next and I am hoping someone will have some suggestions.

Some general observations and measurements:
Compression on MAG side is 125, PTO side is 145 (diff of 20)
Both spark plugs are new and gapped to .021 and I verified that they are firing properly
New fuel filters are in place
carb settings: Low Speed screw = 1.5 turns High speed screw = 0
The pulse line to the fuel pump is the gray type

Some of the troubleshooting steps I took are:
Suspected fuel pump so I swapped fuel pumps between engines - good engine started and ran fine on bad engine pump

Confessions:
I did not test the pop-off pressure on the carbs after I rebuilt them cause I didnt have the tool and I didnt replace the spring - could this be the issue?

Some other questions I have for the experts in the forum:
Why would it start out of water but not in water - heavier load on engine?

No fuel visible squirting into throat of either carb from accelerator pump jet when throttle is advanced rapidly with starter running - Should I see fuel?

If I remove carbs again and dissassemble do I have to replace the rubber gaskets & diaphrams in the carb?

Thank you for your help.

 

[vilord]

I can't answer many of your questions but here's a few tidbits:

Why won't start in water: Yes, the heavier load on the engine needs more fuel to keep it going. Thats why it will idle around 3000-3500 out of water and only 1500 in water.

No fuel visible: There should be fuel visible, according to one of seadoosnipes posts from a while back, not sure which one

If remove carbs need to replace gaskets etc? You have to be very careful not to puncture any diaphrams or rip any gaskets, but if they're basically new and undamaged go ahead and reuse them.

Others will chime in soon with more help, but that should give ya a start

 

[timmyboy76]

that pop-off a "BIG" concern, maybe not changed spring, but if not synced w/ other carb...maybe float arm not level?, needle needs replaced cuz its stick'n,..can rig something up, I used bicycle pump w/ dial gauge. (whether its hard starting, or just rebuild'n carbs, need to check pop-off)
Settings are good..lsa/hsa, nah..on the replac'n gaskets and stuff, if tak'n apart again,..

 

[TXSpeedster]

Thanks for the guidance.

I will pull the carbs off again and check the pop-off pressure, verify needles, float arm, etc.

Timmyboy - do you happen to have a picture of that rig you built to test Pop-off?

 

[vilord]

do you happen to have a picture of that rig you built to test Pop-off?

Take a look at this thread: http://www.seadooforum.com/showthread.php?t=4809 post #6 includes photos of the popoff tester that JPX created for his rebuild. Overall it is a good rebuild guide too!

 

[timmyboy76]

I do, if I can figure out how to download/steal a picture. Idiot when it comes to these p.c.'s. check out JPX sticky under carb thing/whatever its labeled, he has homejobber in pic. Best one is hand bike pump(one's strapped to mountain bikes), I used the foot pump, need couple hands though, but apply til she pops, while watch'n gauge....:cheers:

 

[vilord]

If you can, get a gauge that has a locking/resettable needle, that way when it hits the popoff pressure, you won't have to be watching the gauge as closely, you can just write down the reading then reset.

 

[robin savell lloyd]

Read up on compression I believe you are way out of specks. :cheers:

 

[TXSpeedster]

Take a look at this thread: http://www.seadooforum.com/showthread.php?t=4809 post #6 includes photos of the popoff tester that JPX created for his rebuild. Overall it is a good rebuild guide too!

Thanks for the link, that is a great post and a good picture. Not sure how I missed it! :ack:

 

[robin savell lloyd]

Thanks for the link, that is a great post and a good picture. Not sure how I missed it! :ack:

I believe that you may have missed alot more than that. Please follow up on compression and wait for other responses. :cheers:

 

[TXSpeedster]

Well I finally got a chance to do some more work on the boat and I have an update to this post.

I took the advice of TimmyBoy and pulled of the carbs again to check the pop-off pressure. I was able to cobble together a decent pop-off tester and got the carbs both popping at the same pressure.

I read up on compression and fearing the worst I finally got the courage to pull off the cylinder head to see what I could see.

The good news is that it doesn't look as bad as I thought it might. I have attached some pictures so maybe some others could offer some feedback.

The MAG-side cylinder is the one with the low compression and from what I can see it looks like there is some damage to the piston and or the rings on the side near the exhaust port. Comparing it to the PTO piston it looks like there is a small chunk missing off the top edge of the piston.

When feeling the cylinder wall above the damage I can detect some minor grooves but nothing too deep.

There is no damage that I can percieve to the MAG cylinder head.

Honestly I am not sure what of what to do next. I have no idea of how many hours are on this engine so should I consider a complete top-end rebuild with new cylinders, like an SBT top-end rebuild kit, or can I get by with something less extreme like new pistons and rings only?

I am not an experienced mechanic by any stretch of the imagination but I am not afraid to learn. Is replacing cylinders & pistons biting off more than I can chew? Should I pull the motor out of the boat to do a top-end?

I really appreciate the feedback and assistance provided so far.

Thanks.

 

[timmyboy76]

wasn't bad, was it, stud...good job.
Head looks cool, i'd take cylinder off, take cylinder and head to any engine/machine shop, let them hone it out, and slap new piston in, should have them in stock,..possible, the wrist pin popped off and caused the damage, but think you caught in time. Quik fix, and get back in water...:cheers:

 

[Bent]

Shouldn't the pistons be brought to the machine shop so the machinist can bore to a matching/equivalent diameter?

Oh, also, do the cylinders get bored straight, or do you the keep the top portion of the bore tighter to accommodate thermal expansion?

 

[TXSpeedster]

I pulled off the cylinders to take them to a shop and this is what I found on the MAG piston.:ack: The damage is more significant than what was visible from within the Cylinder.

Looks like both the piston and the rings melted. Was this caused by running too lean?

The MAG cylinder does not appear to be damaged and I plan to take them to a shop to get honed and new pistons fitted. Should I go ahead and the the cylinders bored and get slightly larger pistons?

 

[kustomkarl]

Bring the cylinders to a machine shop and have them mic out the pistons and cylinders to see how big a bore is needed to correct the problem. If it is too big replace the sleeves and pistons/ top end to std, or get new cylinders and pistons and top end. It looks like the engine was was too lean. What do the spark plugs look like?

Karl

 

[TXSpeedster]

The MAG plug does not appear to look burned. It is more blackish than brownish.

Pictures of the plugs are attached.

 

[kustomkarl]

The plugs don't look like it got lean, unless you drove it at a adle to the dock, then the plugs wouldn't mean anything. Get it measured with a micrometer and see what the machine shop says.

Karl