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

  • Thread starter Thread starter makenzie71
  • Start date Start date
M

makenzie71

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...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?
 
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.
 
check the valve clearance first before you condemn the top end as being bad.
prime the carburetors first, what do you mean by that?
 
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.
 
rustybronco said:
check the valve clearance first before you condemn the top end as being bad.
prime the carburetors first, what do you mean by that?
Click to expand...

drop excess fuel into the carbs. Choke has no effect...even covering the bellmouth has no effect...
 
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 said:
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.
Click to expand...

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
 
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.
 
makenzie71 said:
fuel is getting to the carbs
Click to expand...
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.
 
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.
 
makenzie71 said:
drop excess fuel into the carbs. Choke has no effect...even covering the bellmouth has no effect...
Click to expand...

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.
 
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.
 
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
 
makenzie71 said:
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.
Click to expand...
Check your points and set the timing properly.
 
makenzie71 said:
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. ...
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".
Click to expand...


OK so you have had this bike for 24 hours. What is your experience wrenching on other bikes?

Yes, you have listed a couple of items that might make it not run, includind low compression. You know what one of the primary causes of low compression is? Mis-adjusted valves. But...since that can't possibly be the problem, go ahead and rebuild the engine. Don't forget to adjust the valves on the new rebuild.

Oh, and the ignition "problem"? As mentioned by KiwiGS, there is power at all times (when the key is on) to both coils. The points will interrupt the ground, causing the coil to fire. Apparently you have been lucky enough to have the engine stop with the same set of points open any time you have checked it. By connecting or disconnecting a plug, you are completing the circuit and yes, it will fire. There is no problem there, but you may as well replace the points and coil, along with the (probably unnecessary) rebuild.

Sorry if any of this sounds harsh, but we have offered suggestions and you blast them down, then admit you haven't even checked them, so we, as a group, will be moderately offended.

Since you don't know the history of the bike, does it not make sense to check everything? Compression check is a good thing to do. Valve check is supposed to be done every 3000 miles, according to the service manual. When do you suppose they were last done? Points should also be checked every 3000 miles. Again, when were they last done? Have you checked the battery condition and the ability of the bike to charge the battery? Sorry, I guess you can only do so much in 24 hours.
icon_redface.gif


Don't forget that the carbs need cleaning, so you had better buy some new ones.

One other thing:
makenzie71 said:
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.
Click to expand...

1...it probably is NOT necessary
2...the only thing it will hurt is your wallet.

Checking the valves will cost about $10-15 for a gasket, less than $10 for feeler gauges and about an hour of your time. If you need to change any shims, they are less than $5 at Z1 Enterprises.

Rebuilding the top end will cost several hundred dollars for the parts, about $100 for a gasket kit and you will still need feeler gauges, and it will take considerably longer than an hour.

Why not just check the easy stuff and do the harder stuff if, and when, it becomes necessary?

.
 
Last edited:
makenzie71 said:
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.
Click to expand...

1. That compression won't keep the bike from running. That's pretty much agreed on.
2. Sounds like a short in the ignition system.

My advice is to resolve the electrical problem first and see how the bike runs. You can't determine compression with a cold engine, so you can't assume it needs a rebuild until it runs. Remember, these rebuild kits probably cost more than your bike is worth. And if money is no object, just buy a new bike.

Also remember to be patient with people that are trying to help you.
 
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