Stubborn To Start 1979 9.8

[keithb7]

Affer a powerhead refresh, my 9.8 won't start unless I squirt some raw fuel into the carb intake. Then it'll fire up first pull, sound wonderful for a second or two, then die. It seems fuel starved. I have done a couple of real good cleanings of the carb in my ultrasonic cleaner. I pulled apart everything I could. Everything in the carb looks very clean. I hooked up the fuel inlet hose with the carb bowl off. I pumped the bulb primer. I manipulated the float by hand. I can see the float and inlet needle & valve are working properly. There is fuel in the bowl. The black plastic ventui is in the carb is present and looks good. The engine just doesn't seem to pull fuel through the carb as it should.

To recap what I did to this powerhead:
Disassembled engine & measured pistons and bores
Honed cylinders
New piston rings OEM
New crank seals OEM
New crank bearings
All new reeds, OEM ( I believe reed block can only be installed 1 way)
Cleaned & gapped spark plugs
Can visually see good strong spark at plugs
Cleaned plug wire connections at plug boots and coils
Set static timing to spec
Disassembled and Cleaned carb in ultrasonic cleaner 2x
Current compression measured at 75 psi, rings not broken-in

I've tried multiple variations of choke, throttle and idle screw adjustments with no improvements. I gave up tonight after the knot in my pull starter handle opened up. All the rope sucked inside. Lol. I'll open that up tomorrow and re-set the rope again. Does anyone have any suggestions or ideas what may be going on here? I'm told 75 psi is normal for the comet and lightening powerhead units. I've hit a wall with this problem. Unsure what is causing the symptoms. Thinking I may swap the carb out with the one off my 7.5. It seems to work good. See if the 9.8 will fire up after a carb swap.

Thanks in advance for any suggestions.

 

[keithb7]

The issue appears to be compression. I put oil in the cylinders and raised compression to 110 psi. She’ll run. I’ll see if seating the new piston rings will improve it.

The cylinder taper and out of round was well within spec. Pistons looked great. Stock bore. New rings and honed cylinders. What do you feel is the issue here? Are these fussy engines that need near-perfect, new cylinders and pistons? Maybe seating the rings properly will do it. Working thru that now. Thx.

 

[rolmops]

It is fuel starved for sure. Sounds like a fuel hose connection or a defective fuel pump.

 

[Nordin]

Just a "long shot", have you change the gasket between the carb and the intake manifold?
I have had this kind of issue with a Mer 200 20Hp.
You have to set the gasket in the right way as there is a little hole in the gasket which is for the crank case pulses to drive the fuel pump.
I suppose your engine has the fuel pump integrated with the carb.
I think the 9,8 Hp and also the 7,5Hp has the same kind of carb with the fuel pump mounted at the left side of the carb.

 

[Mc Tool]

Sure does sound like fuel starvation

 

[keithb7]

Thanks for your responses folks. I feel like I solved it. It was indeed low compression. I lightly honed the cylinders and installed new rings. Compression test dry, netted 75 psi.

I pulled the plugs and put some oil into the cyliders. I pulled it over a few times to coat everything. All the micro grooves from honing were filled. Compression test now showed 110 psi.

I put the spark plugs back in and it fired up first pull. This tells me the new rings need to seat and break-in. I need to do this with the engine under a load. I’ll get my boat out on the water this weekend and do that. I fully expect the compression to rise and then rings seal.