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79 9.9 seahorse idle warm issues

P

poida

Contributing Member
Hi all.
My neighbour dropped his 9.9 (10r79b) to me with idle issues and a pain to start sometimes.
I dropped it in a barrel of water and it started first pull with the choke on, pushed choke in and it continued to run. Working like a charm. In neutral you can give it a bit of throttle and i revved it up and down and all seemed good. I noted that the engine had a bolt to stop you retarding the timing and at lowest revs the throttle blade was just shut. When giving it a rev up it it was slow to respond, i thought maybe it had dropped a cylinder but putting it in gear and revving it it had plenty of balls.
I put a spark plug tester and had spark across both cylinders with about a cm of airgap. (have not checked colour at night)
Compression 90psi on bot pots. (can start easily first pull so this seems good)
Popped flywheel and keyway is fine.
Disconnected kill switch.
Rebuit carb, popped out welsh plug and made sure 3 holes for idle circuit are clean. Could not get small white plastic seat for the needle out, tried easy out and screws, not sure it ever had one so put one in anyway.
Again motor started first pull and kept running. After a minute or two it started to be slow to respond to the throttle. A slight squirt of fuel down the carb throat seemed to help most times. Then suddenly it would cut out and refuse to start. Rechecked spark repeatedly and ran engine till it cut out again. Even after pulling plugs and turning over then reinserting plugs it would not fire sometimes.
Threw compression gauge on it again and got 70psi on each pot. I thought this would have gone up when warm????? This could be the cause i would assume.
Thoughts people??? This has me scratching my head.
Cylinder head?
lower crank seal?
Reid Valves?
Fuel filter gasket.
I have squirted fuel around the motor to se if its sucking in anything anywhere but no change.
I am leaning towards head gasket but don't want to do it unless i have to.
 
Did you try pumping the primer bulb or is the primer collapsing when it slows down? Kinna sounds like a dirty strainer in the tank or the pickup tube. Try disconnecting the fuel line at the tank and stick it in the tank and see if it keeps running better?
 
The bulb primes as per normal and i have tried pumping it when the problem occurrs, it is hard at this point in time. Its now running off my tank not the owners so it is not the tank. I do like the idea so will check fuel pump strainer and flow to carby when the problem occurrs.
 
Fuel pump strainer is fine. She started well and rev'd up and down although it seems to rev up slower than it should (timing is all good) after a few minutes i rev'd up (still in neutral) and she refused to lift above idle, then conked out. I pulled the fuel hose off the carb and gave it a few pulls and fuel is flowing out. I would assume that she would rev out (lean rev up) if it were a running out of fuel problem, she just seems to conk out like the timing is retarded too far, no lean sneeze either.
Still thinking its a compression problem when warm?
 
Its pumping water fine, i can't smell any burning and she certainly is not seizing up, i'll get the temp gun on her tomorrow.
 
You mentioned:
"I noted that the engine had a bolt to stop you retarding the timing"
Click to expand...
and
"she just seems to conk out like the timing is retarded too far,"
Click to expand...

Can you check timing marks against the true TDC of piston #1 and then use a timing light to check the time setting and advance action.
Art
 
There is no timing adjustment just engine sync or throttle pickup adjustment. With the engine off put it in forward gear and advance the throttle until the follower roller is center of the two marks on the throttle cam. It is at that point the throttle butterfly should begin to open as you advance the timing. You can make that adjustment exact with a alligator clip and a paperclip crimped in the end. Clip the alligator clip to the throttle butterfly shaft it will tell you exactly when the butterfly begins to open then slowly watch the marks on the throttle cam as you advance the timing from slow when the roller passes center of the two marks the butterfly should just begin to open on the carb. The only thing that will throw the timing off is a loose plate under the flywheel or a sheared flywheel key!
EDIT Make sure the flywheel is torqued to spec just a small crease in the key will throw the timing way off.
 
Last edited:
Timing is all good, flywheel is torqued to spec. Armiture plate is moving like it should.
Why is my compression lower after a few minutes of running??? Surely this should be higher???
 
Ok, i pulled the motor from the body and replaced the head gasket (sanded the head flat) and replaced the exhaust cover gaskets at the same time to help the cooling system.
It started on the 3rd pull and ran fairly well, i tried to idle it down and correct it with the needle and only the last 1/3 of a turn seems to affect the idle. This has made me think its running rich. After it stalled it refused to start so i checked compression and got 90 on the bottom and 80 on the top. It then started, again after stalling it was a pain to start and i thought it was flooded but i choked it and it ran again.
Definately have a carb issue still through the idle circuit. I might try the carb off a 9.9 that has been unused for many a year and see how it goes.
Might have damaged the needle seat trying to get that plastic seat out (which i don't know if it came out or not)
 
I found a 15hp carby and gave it a clean out, fitted it to the 9.9 and she started 3rd pull. It still seems to me to be a little slow to rev up after twisting the throttle. She ran well for 5 minutes then i rev'd her down and set the idle screw. I did get a lean sneeze and it seemed the best position was the 1.5 turns out from gently seated. If it stalled she would start with an easy half pull and i was pretty stoked. Then she stalled and would not start!
Pull choke out, 2 pulls, can fell catch, push choke in, pull, rev's up then dies. Repeat and Repeat.
Can hear a soft (pop pop pop) noise when she dies that is comming from the pee tube.
Compression on both is 85psi (warm)
Spit dummy and give up.
Ran pretty well for 10 minutes then went to a choke only start then rev and die.
 
The engine sync is properly adjusted, i did get it to idle with the butterfly fully closed but this was only just and seemed to get worse towards the end of the 10 minute run. I can imagine that 85psi could contribute to an idle problem, but not this conk out and refuse to restart problem.
This little motor pushes a 16ft fibreglass boat and i have had 2 props with less pitch to help it out, the shims would be a good idea but pointless unless the motor can run for more than 10 minutes.
Pumping the primer bulb did not help. It really does seem to be a fuel to the cylinder issue i think as it tried to run/start when i choked it yesterday. (not that i should need to choke a warm engine)
The cylinder head regrind seems to have my compression stable, (also cooling system working a treat)
2nd carb has helped with rich lean screw and being able to idle it down (still not great but could be compression)
Something is going wrong when it heats up and it seems like a fuel delivery issue.
 
Put some dish soap in a spray bottle and spray all over the engine while running. If you see bubbles it is a leaking gasket possibly gets worse as it warms up. Did you install a new carb gasket? Surface the flange on the carb on a glass table with 220 grit paper just pull it in one direction only. Make or buy a new gasket and do not overtighten the carb down nice and snug is all thats necessary. Allways use a new gasket when mounting the carb. Compression should be good for a pull start anything over 70psi is acceptable.
 
If you cannot hold your hand on the head for a slow count of six any time the engine is running you need to figure out why it is overheating. It should get hot enough you want to pull your hand away but dont have to.
 
It is real important to get the flange nice and flat and install a new gasket. Be sure and adjust the sync after you install the carb!
 
That is a big boat for a 10hp the 15hp carb will help. If you get it running good be sure and get the spacers for the leafs and install them. Otherwise you can damage the motor running too lean due to the larger venturi in the 15hp carb. pushing a barge it probably wont hit a decent plane but if the motor is reving too high more pitch on the prop will cure that.
 
I sanded the carb flat and installed a new gasket. Started her and it ran good for 10mins or so. Whilst walking around and squirting the engine down with soapy water i walked into the shed. At this point i heard her rev down, then she picked back up by herself. I thought i heard her change note a few times (soapy water had nothing ot do with this) and after ten minutes she tried to die. I had my hand on the tiller and gave it full throttle in neutral, it idled for a bit (like on one cylinder not reving up)then did rev up and died, would not restart. I thought it did seem a bit like a cylinder dropping out so i changed the coils over with another motor. It started ran for a few seconds then died and would not restart. I changed the plugs over, again it ran for a few seconds and died. At the moment if i walk outside it will run for a short amount of time then die (depending how hot the motor is)
I am thinking of changing out the power pack, any other idea's?
Also check at night for spark colour.
 
I switched powerpacks and had no luck.
After sitting for an hour it ran for only 10 seconds, so i thought the fault was present.
I put the original pwr pack, coils and sparkplugs back in and it started and has been running now for 15 minutes.
Reving high in neutral the top of the head gets to hot to touch for 6 seconds, the block is fine. Temp gun gave me a heat of 70dg.
 
I rev'd it down and the fault has come back. Twisting the throttle grip might be part of the problem, (although choke can help) could it be driver coil under flywheel?
 
Perhaps a bit of closure on this problem.
I found/made some time and think its sorted.
The bugger ran fine for 5 minutes then lost rev's, up and down and stalled. This was a bit like loosing spark on a cylinder but slower to loose rev's.
Pulling the boots off the plugs the upper coil would arc out through a crack whilst running. The engine was not running off one cylinder although i pulled both boots when it idled down on its own. I replaced the coil out of frustaration, not that it was atributing to the problem.
 
It would start and run for 5 mins, then rev down and up then down and stall.
This was now like clockwork, it did seem like a fuel issue. I could repeat this time and again. Priming the bulb had no effect.
I replaced the fuel pump and the problem is now gone.
I can only suspect that once warm the fuel pump would pump fuel into the cranckase makind the motor stall and not start.
Since swapping out the pump it has run flat out for 40 minutes and idled down happily.
Thanks to all.
Head gasket leaking
Upper coil arcing out (probably not contributing to problem)
Carby idle jet stuffed
Fuel pump leaking air/petrol into motor when hot.
 
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