Erratic idle 787

[lilngineer]

Wonderful!

Another problem....

Today I noticed my 787 is idling weird after driving it.

It wants to go down to about 1k and jump to 1600 and back down etc.

Any thoughts?

My whole engine is rebuilt. Carbs, crank, pistons, rings, jugs etc.

Electrical maybe?

 

[chuckydoo]

I have the same problem with my 1996 spx. I just rebuilt the entire engine cran and all. I'm thinking air leak somewhere. I going to have to take off the carbs and maybe the rotory cover and reseal.

 

[lilngineer]

Please keep me posted.

Tonight I replaced plugs and recleaned the carbs meticulously.

Test run tomorrow....

 

[timmyboy76]

what about fuel lines?

 

[lilngineer]

Fuel lines were changed about a month ago for good measure.

Got it out today again and no luck. Same problem.

When I start it cold/on land it idles smooth.

I take it for a ride (up to WOT), runs great.

When I bring it back down, tach goes to 1K or lower. Occasionally it jumps around up to 1500 where it should be.

I rechecked carbs and replaced plugs. Any other ideas???

 

[lilngineer]

One more thing...

Letting it sit seems to bring the idle back up, but it still sounds like maybe it's missing to me. I hear an occasional stutter in the idle.

 

[timmyboy76]

lil....take carbs apart, and bend "tang" down slightly. and/or inspect the needle. also, inspect the inline filters' o-ring/replace with "regular" inline filter.

 

[lilngineer]

Timmy,

I tore them apart yesterday. Everything looks nice and clean.

I did check the needles/seats/tangs.

Ok, here's another observation. Coming down off WOT, and bringing the control back to idle the RPMs are dropping to about 700. It stays running, but occassionally jumps up to about 900-1K. If I rev it a few times, it sometimes jumps back up to around 1500. But even there it jumps up and down about 200 and sounds like a miss.

Can i give you a call Tim and let you hear it while I'm on the water? You can PM me your number.

 

[Cid6.7]

While your out & its actin funky take a can of WD with yah spray around known air leak areas if it sputters more you suckin in air..

 

[lilngineer]

Could it be that the carbs are not popping correctly?

Although, it doesn't explain why the problem suddenly appeared.

Driving it while the symptom exists, it seems to have no power until I am up to nearly half throttle and then it feels like it kicks in.

 

[chuckydoo]

Here's my update. I found out it was a crank seal leak. I just put the crank in last week. The company is sending me another one next week. I finally decided to make a block off for the exhaust and used rubber expanding plugs for the intake. I pressurized up to 5 lbs and I saw the oil and bubbles rushing thru the rotory valve oil lines. It seems the inners seals are not holding. Yours sounds alot like a air leak also.

 

[lilngineer]

Chuck,

Where did you get your crank from?

And where did you get the rubber plugs for the intake?

 

[chuckydoo]

Hi, rubber plugs where from Home depot. 1 1/2'' work perfect for my engine. the crank came from playtime sports in I beleive clearwater, Fl area. They have a E-bay site.

 

[lilngineer]

Interesting....

My crank also came from playtime.

How did you block off exhast? With the manifold gasket and a plate?

 

[lilngineer]

I found a way to reproduce it on the trailer.

I start it, engines goes to 3k, I put it in forward and give it a quick rev. On the way down the idle goes low (~500RPMs). If I shut down and immediately start, it seems to stay at low idle. Rev a few times and I can sometimes get it to stay up.

I removed, checked and reinstalled the carbs again tonight with no luck. I also tried disconnecting the red wire on the rectifier but no go either.

Trigger maybe?

 

[lilngineer]

86 the trigger idea; seems fine. Static test is 252 ohms. Cranking was 0.8VAC.

I also checked the coil, wires and boots. All ok.

 

[chuckydoo]

for the exhaust block off I just traced the gasket on 3/4" oak I had lying around cut it with a jig saw and drilled the holes works great. I used the original gasket under the block off.

 

[lilngineer]

Aren't the sypmtoms of an air leak high RPMs especially out of water?

Mine is not that way at all.

 

[chuckydoo]

Your right, most time with an air leak you get a runaway idle or its very slow getting back to an idle after you rev. Hopefully that is not your problem.

 

[lilngineer]

No, my RPMs fall off when coming down from WOT.

I am going to make sure the RAVEs look ok today.

I was hoping to be boating over the holiday weekend, not repairing!

 

[lilngineer]

RAVEs recleaned with no change.

I have a new observation. The service manual details a test for the rectifier. Basically, disconnect red lead and measure voltage to ground. Spec calls for 13.5-14.8VDC @5000RPMs.

When I did this, there was no improvement by disconnecting the red lead but the measurement started near spec once started and then went crazy. It goes up to 30-40V and then goes to a negative voltage.

Wondering if this could be related, but I thought disconnecting the red lead disables the rectifier.

Or could it be the stator?
*

 

[chuckydoo]

If its related or not it still sounds like a problem. I thought the rectifier only effected the battery charging. Its very fustrating working on these things. I just took out my other ski which is a 1995 Seadoo GTX and it ran for a while and then just quit like it ran out of gas then it would restart run for a few seconds and do it again, finally wouldnt start at all. Not so fun day at the lake. I'm ready to give up on these beeping machines. You can be chasing a ghost for a while, might be better to just take it to a shop and have them fix. Sounds like your not regulating the voltage. Maybe the rectifier is bad?

 

[timmyboy76]

lil...good job, man..give that a shot. Leave the red wire disconnected, and go hit lake. Make sure, your battery is good/charged, since with that unplugged, no juice is going back to battery to charge it.

 

[lilngineer]

lil...good job, man..give that a shot. Leave the red wire disconnected, and go hit lake. Make sure, your battery is good/charged, since with that unplugged, no juice is going back to battery to charge it.

Timmy,

Actually pulling the red wire didn't work.

BUT...

Someone locally had a used one. I just put it in and guess what? I works!!

Problem solved (pending a lake test).

 

[lilngineer]

Spoke too soon. Problem is still there!