90...75...90...115...

[makenzie71]

...that's what my pistons are punching out on my 1979 GS750E. Fun. I can get her to fire up...briefly...and only if I prime the carburetors before I try.

Does anyone sell an all-inclusive top-end kit?

Also, the #2 and #4 plugs have constant juice to them...they're the same coil, iirc...what would cause this?

[tkent02]

1 and 4 are on one coil, 2 and 3 are on the other coil, or should be.
Are those compression test numbers? if so, they seem low but maybe the engine is still OK. If it wasn't running obviously the engine wasn't warmed up, if it hasn't run in years it cannot have high compression, I would suggest getting it running and riding it several hours, redo the compression test hot. Also did you do a wet test as well?

That compression is certainly enough to get it running if everything else is working properly, and then you can ride it around some.

But if it does need a top end, Wiseco has a kit, makes it an 850. Or you can get cylinders and pistons from an 850 and do it yourself, the Wiseco kit gives a higher compression ratio.

Whatever you do don't buy parts from Ridenow, they won't send anything for months.

[rustybronco]

check the valve clearance first before you condemn the top end as being bad.
prime the carburetors first, what do you mean by that?

[makenzie71]

If I go with the kit do you have any info on who to buy from? I'm curious about how much and what all it includes.

Double checked and yeah two coils...one for 2 and 3 and one for 1 and 4. The coil for 2 and 3 has constant voltage going to it.

Wet tests all jumped about 20lbs...except the 115lbs one. That one only picked up about 10lbs...if that.

Bike was last registered in 2002. It hasn't been a street bike in years...lawn ornament for most the time off. I have ATF sitting on top of all the pistons right now. I'm going to try and get her going tomorrow...if it's stuck rings the tranny fluid will break them loose.

[makenzie71]

check the valve clearance first before you condemn the top end as being bad.
prime the carburetors first, what do you mean by that?

drop excess fuel into the carbs. Choke has no effect...even covering the bellmouth has no effect...

[rustybronco]

How long since it last ran?
fuel getting to the carbs?
open a drain screw on the bowls and see if fuel is getting to them.

[makenzie71]

fuel is getting to the carbs

[KiwiGS]

If I go with the kit do you have any info on who to buy from? I'm curious about how much and what all it includes.

Double checked and yeah two coils...one for 2 and 3 and one for 1 and 4. The coil for 2 and 3 has constant voltage going to it.

Wet tests all jumped about 20lbs...except the 115lbs one. That one only picked up about 10lbs...if that.

Bike was last registered in 2002. It hasn't been a street bike in years...lawn ornament for most the time off. I have ATF sitting on top of all the pistons right now. I'm going to try and get her going tomorrow...if it's stuck rings the tranny fluid will break them loose.

Mate.
The coils should have voltage on the 12v side when the key and kill switchs are on. The points/ignition break the voltage briefly.
You need to get a meter and check the the resistance of the coils.
Should be about 3 ohms on the low side. (power off)
Cheers

[makenzie71]

no no no...it has voltage going through the spark plug. I know they're supposed to have 12v supply. If there's supposed to be constant voltage flowing through the plugs then the 1 and 4 coil isn't doing it.

[rustybronco]

fuel is getting to the carbs

Lawn ornament, time to dis-assemble them.
take a spare plug stick it into a plug wire lay it on the head, crank er over and check for spark.
do the same for the other ones.

[makenzie71]

it's getting strong spark on all four plugs in correct time.

The further explain the coil issue, though...when the key is on, if I take a spare plug and put it into the #3 or #4 boot and touch it to an earth point, it will arc without the motor spinning. It I grab the plug while touching an earth point it'll shock the **** out of me without the engine spinning. All it needs is the key to be on.

[tkent02]

drop excess fuel into the carbs. Choke has no effect...even covering the bellmouth has no effect...

So the carbs are thoroughly clogged, the valves have not been adjusted and are likely not closing, and the ignition isn't working.

So why won't it run?
Yeah, rebuild the top end, that'll help.

[makenzie71]

One set of plugs isn't working properly, in my opinion...I do not know. No one's told me that my situation is unusual as of yet.

You have no better idea than I do that the valves aren't closing. Maybe they are...maybe they're not. I've had the bike less than 24 hours.

The carburetors are flowing just fine. If I cover a bellmouth it blows fuel all over the place. The engine isn't providing enough suction to pull the fuel through the jets.

I've listed the reasons why it won't run: low compression and a possible ignition glitch. I never asked "why won't it run".

It's a 30 year old machine. I'm looking at rebuilding the top end because:

1...it may be necessary.

2...it can't hurt anything.

[tkent02]

Cool, have fun.

[80GS750]

feeling vacuum at the mouth of the carbs will get you nowhere... just trust me.

pull the carbs off and crank it over, you will feel hard vacuum in the intake holes....

the compression will come up if you get it running and do a proper check with it HOT and WOT

did you clean the carbs? without properly disassembeling them and cleaning them thoroughly and putting in new O rings, you cant be sure they are working correctly at all...

you definately have an ignition problem.... i would check the points and make sure they are working properly, those cylinders should not be firing when you just ground them out....

do you have a manual? if not, i would get one cause it will answer most of your questions