Fuel/electrical issue...1979 GS750

[Guest]

Bike:

- 1979 Suzuki GS750 Base (wire wheels single front disc)

Timeline:

- Bike ran well yesterday morning for about 30miles.
- bike did not run well last night about 6pm.
- bike sat for ~6 hours between rides

Symptoms Last Night:

- bike will only start with choke on
- bike will rev up to 2.5k then immediately die
- bike will not start without choke

I fixed this issue, or so I thought, by adjusting the points. The left side was wide open and right side was shut. I fixed these to "matchbook cover" thickness and it fired right up. This was earlier today. Tonight I took it for a ride, and while it runs now, it still isn't right.

Current Symptoms:

- bike will start with choke, and eventually run on gas
- bike is VERY slow to build revs
- bike bogs down starting in first gear
- bike will not rev past 4.5k RPM no matter if I have throttle wide open or not
- bike needs to stay revved or else it'll die

Things I've Checked:

- Petcock has great flow
- battery is fully charged
- points are set
- Petcock was taken apart and rebuilt last night

Questions:

- is this fuel or electrical related? Given that the points reset helped things along I'm inclined to believe that it's electrical. Does that mean I'm looking at a R/R upgrade or EI?

- what is my next best course of action to identify my issues?

Thanks,
Matt

[Big T]

Points - gap and reset timing, replace as necessary

[mattfeet]

I reset the points gap tonight. I'll look into timing tomorrow. Thanks!

[JAG]

Points - gap and reset timing, replace as necessary

Agreed. Check all components and reset to factory specs.

[mattfeet]

I'm being told on another forum to look into the plugs. Thoughts? I have a hard time believing that all 4 plugs can foul at the same time causing it to run badly.

[exdirtbiker]

I'm being told on another forum to look into the plugs. Thoughts? I have a hard time believing that all 4 plugs can foul at the same time causing it to run badly.

Probable that something HAS fouled your plugs.. but that is a symptom, not a cause.
remove the cause, and the symptoms go away.

[simon kuether]

Mine (in Ohio) did a similar thing .
Ended being a condenser on one set of points .
Josh (who's being flogged on another thread) and Steve replaced the points with a Dyna set up and the bike hasn't missed a beat since .

Goodluck .

Cheers , Simon .

[Big T]

I'm being told on another forum to look into the plugs. Thoughts? I have a hard time believing that all 4 plugs can foul at the same time causing it to run badly.

That's why this is the best place to come for advice

Yes. it is hard to foul plugs on a 4 stroke, much less all 4

Replace your points and condensors

[mattfeet]

Today I replaced the condensers with spares I had and it has the same issue. Cylinders 1 and 4 run hot to the touch (header pipe) and cylinders 2 and 3 are barely warm to the touch. I reset the points, again, as well.

[mattfeet]

I just went out nd bought 4 new spark plugs (more for maintenance than anything) and will be replacing the 2/3 coil. Im pretty sure that should be the culprit to all of this.

[Coady]

Don't want to sound rude, but you are setting the points with a feeler guage and the then checking the timing with a light or circuit of some kind?

"Matchbook cover" thickness isn't good enough and the timing is just as important as the points' gap (well they're inter-related really). It has to be spot on or you will get the symptoms you describe.

Please do this again before you throw money at coils.

[mattfeet]

Funny you say that...I did some more research and will be doing just what you described this week.

[mattfeet]

Bought a feeler gauge and reset the points last night. The OEM thickness was too wide for them to both spark reliably so I lowered it 2 steps down and now the bike fires perfectly well. The points look to be original ('79) with 22k miles. I ended up ordering a Dyna-S setup for the bike so I can get rid of the points altogether. All coils, condensers, etc., checked out fine. In fact, my coils have been replaced at some point in time with much newer looking Denso units.

-Matt