Runs rough after engine swap

[Anonymous]

I just swapped an '82 gs1100GL engine into the '79 GS850G frame. I had to swap over the ignitor and coils (just in case the latter were different). A few other modifications required to control cables, but other than that the swap went smooth.

Anyways, before the swap, the 1100 engine purred smoothly. Now after the swap it runs rough at best (although has more power than the 850). The odd time it spits and farts and seems to clear up under acceleration but not always and even then it is still rough. The carbs were not tampered with and the inlets sealed with silicon grease so I don't think there is a leak. I can hear one of my exhaust headers leaking a bit, but I can't think that would cause that much of a problem. I am inclined to think electrical over carbs unless someone wants to correct me. Any suggestions?

[Mark Harrop]

sputtering

I usually check for spark before I rip the carbs off, its the easiest thing to troubleshoot.

[Anonymous]

Thanks,
Spark is there, but I can't tell if it is intermittant. Any suggestions as to tell how consistent the firing is?

I think cylinders 1 and 4 might be running a bit cooler than the center cylinders, but that might be that the outside cylinders get better cooling.

I agree, carbs are a bit unlikely, especially since they were running fine in the previous bike.

The bike is running and has power, but just doesn't run smoothly. And not quite the same power as the GS1100G that I have been helping my buddy just bought.

[robinjo]

How does the airfilter element look? Dirty? What color are the sparkplugs?

[Guy]

Just a thought.............is the stock airbox on the 850 similar to the 1100? Maybe it isn't passing the same volume of air. As for engine temp, the outside cylinders always run a few degrees cooler than the inner ones.

[Anonymous]

Guy, I moved the 1100 airbox with 1100 motor. I also moved the ignition system (ignitor box), carbs, drive shaft, throttle control and choke control (with some modifications) and coils. I mention these in case anyone else might be interested in doing such a swap more than I think they are affecting the performance right notw. I am suspicious about the electrical stuff though, mostly because this is not an area I am very knowledgable about.

Robinjo, the air element is clean, the spark plugs vary from only slightly sooty on one with the other three being grey/tan.

The wiring harnesses are a bit old and may be giving me trouble. I am considering rebuilding them over buying new harnesses. There seems to be significant voltage drops through the wiring. I suspect that this is more to do with the Suzuki wiring rather than age and am considering heavier gauge wire. As an aside, I am also thinking of using a relay to the headlight as I only get just over 9 volts at the headlight.

Anyways, back to the problem, what do you think that the problem may be in the wiring harness (old brittle wires, poor connections, etc.) Since lighting seems constant when the bike spits and belches, perhaps Kill Switch circuit, coil circuit, something like that????

[Guy]

Yeah, I agree the original wiring on these old bikes is pretty dismal, the only thing that really lets them down. The headlight relay mod really makes a difference. One of these days I'll get around to making a whole new loom for my own bike. Sounds like your problem could be electrical all right. You could try temporarily connecting the coils (through a 10A fuse) direct to the battery. Make sure the battery's fully charged first. Worth a try. Good luck.

[SqDancerLynn1]

I would give the carbs a quick cleaning, being they were off the bike any junk in the bottom of the carb bowls could now be in the jets

[Anonymous]

My brother and I spent the morning playing with the coils, checking out power through the kill switch and ignition switch. Everything checked out. Removed the carbs, cleaned them out, there was a little bit of gunge in the float bowls but the main jets and emulsion tubes looked fine. Blew out all the ports. Not alot of difference. We noticed that the carb slides fluttered erratically. Finally my brother went to the ignitor module and added a new connection to ground. Noticed the carb slides fluttered less violently. Low and behold the bottom end was great, but it couldn't get above 3500 RPM. Took the carbs back out and checked the diaphrams, they looked fine. We had been checking the bike out without an airbox on. And then it occured to my brother, suppose the slides are prematurely lifting because of too much air flow. No matter how I approached the higher RPMs, it just couldn't get over 3500. So, thinking it might be too much airflow, I put the airbox on for further testing and IT TOOK OFF LIKE A ROCKET. Gravel spewing everywhere. What a hoot. I came back with the biggest smile on my face. My brother took it for a spin, he came back shaking (that means he was very happy).

So, I think the problem was initially a poor ignitor ground but further problems occured because I was testing without an airbox.

Has anyone else found out that increasing the airflow too much like this has a detrimental effect on the top end?

Thanks for your help people. With the little information I gave you, I think you were on the right track.

Hope this might help out others. I know I have learned things just by reading past posts. And for this, I also thank you all.

[SqDancerLynn1]

Glad you got your bike running NONE of the GS bikes will run correctly without the airbox

[Anonymous]

Airbox fitting

Glad you got your bike running NONE of the GS bikes will run correctly without the airbox

NOTHING runs quite right without an airbox, it's just that Mikunis and Keihins are particularly fussy. Everything is jetted or adjusted with the loss of air flow from filters figured in. Even a Briggs and Stratton will run lean without a filter. When you take the filter and box out of the equation, you dump massive amounts of air directly into the combustion chamber, leaning things way out. The carbs cannot adjust themselves like fuel injection can with computers that monitor O2 sensors hundreds of times a minute. That's why pod filters need jet changes, they flow much more air so when you up the jets with it, you get more power to the limit of the exhaust. Bob

[Anonymous]

I see your reasoning. But I have done troubleshooting in the past with out such severe consequences. This is the first time I've played with CV carbs. I suspect that it was this that totally wiped out the top end. I mean TOTALLY, it would not go above 3500 RPM. With the older style carbs (as the set on my old GS850 engine) the effect was no where near that severe. Does this later style of carb suffer the effects more severely?

[moto_dan]

Glad you got your bike running NONE of the GS bikes will run correctly without the airbox

NONE????????? That's a pretty broad brush stroke of generality. I guess it all depends on one's definition of correctly.

[Anonymous]

Glad you got your bike running NONE of the GS bikes will run correctly without the airbox

NONE????????? That's a pretty broad brush stroke of generality. I guess it all depends on one's definition of correctly.

Me thinks she meant to add "with stock jetting taken into consideration" 8) Bob

[moto_dan]

Glad you got your bike running NONE of the GS bikes will run correctly without the airbox

NONE????????? That's a pretty broad brush stroke of generality. I guess it all depends on one's definition of correctly.

Me thinks she meant to add "with stock jetting taken into consideration" 8) Bob

You're probably right. I was just afraid my '83 would read it and demand me to reinstall the air box