Help a noob? '79 XS1100F

[jdub89]

Hey everyone, new guy here! I joined the original forum when I got my XS11 about 15 months ago before realizing the site was basically dead. Glad this popped up with some active members again. Hoping to get the ol' girl back on the road.

According to my VIN, I have a 1979 XS1100F with an engine out of a 79 XS11 Special. Unsure of engine mileage but the bike shows around 9500. When I got the bike it had leaking carbs(in crankcase and airbox), nonfunctional petcocks, a backyard oil cooler, missing the octopus valve but currently has the fuel hose from petcock routed direct to carb with carb boot nipples capped off, and a slew of wires hanging about. I cleaned the carbs the best I could and rebuilt with new carb kits, replaced carb boots to engine, rebuilt the petcocks, connected wires back according to service manual diagrams, drained oil and changed oil/filter, removed oil cooler and replaced with OE line under carbs, replaced spark plugs, rebuilt calipers and installed new pads/brake lines, and replaced brake/throttle/clutch cables.

I am having issues keeping it running...it backfires pretty regularly...and when I had it running the best, i had minimal power from idle to 2500rpm..plenty of power between 2500-4500..and another loss of power after 4500. I had to put this on the backburner for awhile, but I am finally getting back to it. I am hoping someone here can shed some light on my issues. I have a mechanical background but mostly with cars not motorcycles.

Today I tested my coils. Both are at about 15k on the plug side, but I was having trouble testing the harness side. Manual says 1.5ohm spec but I was getting about 2.2ohm. I have another set of used coils that test the same so either that is within spec or both sets are bad. I'm going to have my battery tested but will probably replace anyways just cause. I don't have a compression tester but I'll probably pick one up soon to be sure I have it on all cylinders. It appears fine but you never know. I have checked my timing at TDC, but I don't have that little metal pointer under the cover so I used my best judgement based on the pics in the manual.

Anything else I should look into in the meantime? Figured I would ask cause I know every old bike model has its quirks. Hoping one of you have dealt with this issue before. Is that octopus valve thing mandatory or do people remove those with minimal issues? Thanks in advance!

Cheers,

Jeff

[jkorn]

I would start with a complete carb rebuild. there are several places where you can get kits for that. Lay everything out and do not mix parts from one carb to another. Stock main jets are 137.5 I replaced the with 140. Make sure float height is correct. Verify which notch the main needles are set al. Clean the hell our of all the really small passages inside the carbs. Finally synch them. Jeff..

[bikerphil]

That bike is an SF, not an F. The Vin should start with 3H3, not 2H7.

[DiverRay]

And you are running lean, by the header pipes changing colors. Jeff gave you a good starting point on the carbs, and I would go to brakes next. Running is great, but stopping is better!

[jdub89]

That bike is an SF, not an F. The Vin should start with 3H3, not 2H7.

Yea, that is what I saw when doing research on the VIN. This bike is an F. Frame VIN is 2H7, engine VIN is 3H3. My assumption is that an SF was sacrificed for my bike. Tank, engine, and side covers appear to have been swapped over. Perhaps more?

[jdub89]

I would start with a complete carb rebuild. there are several places where you can get kits for that. Lay everything out and do not mix parts from one carb to another. Stock main jets are 137.5 I replaced the with 140. Make sure float height is correct. Verify which notch the main needles are set al. Clean the hell our of all the really small passages inside the carbs. Finally synch them. Jeff..

Is it best to contact Mikuni for this? I have already rebuilt and cleaned the hell out of everything, but I did not swap the emulsion or diaphragm (all the rubber was in great shape). Probably could use another run through now from sitting, but even when all was fresh I had the same issues.

[jdub89]

And you are running lean, by the header pipes changing colors. Jeff gave you a good starting point on the carbs, and I would go to brakes next. Running is great, but stopping is better!

I will look into the carbs some more. The header pipes changed colors back when I first got it running before going through the carbs the first time. Hasn't run much since then. The brakes have all been done minus new rotors. Mine were in good shape. Front and rear calipers and master cylinders have been disassembled, cleaned, and rebuilt with new parts/seals. Stopping is not an issue...I just need it to go!

[bikerphil]

Where are you reading 2h7 because that is a Special frame, I can tell by looking at where the rear brake pedal connects, the Standard 2h7 frame is different in that area.

[jdub89]

Where are you reading 2h7 because that is a Special frame, I can tell by looking at where the rear brake pedal connects, the Standard 2h7 frame is different in that area.

Here is a picture my frame and engine stamp. Also this bike is titled as 2H7.

[cajun31]

Here is a picture my frame and engine stamp. Also this bike is titled as 2H7.

so... you have a 79 standard frame and a 79 special engine. Do your carbs look like those that Jeff posted? By the way I agree with Jeff on cleaning the carbs regardless of what year you have. An ultrasonic cleaner would help. From the symptoms you described on how the bike ran I would suspect carbs. When you rebuilt them what kind of kits did you use and did you replace all the jets with the kits? If you did then you would be better off with Mikuni jets which are available from JetsRus. If you can post pictures of the carbs. When you went through the brakes did you completely disassemble the master cylinders and verify all the seals were good?

[jdub89]

so... you have a 79 standard frame and a 79 special engine. Do your carbs look like those that Jeff posted? By the way I agree with Jeff on cleaning the carbs regardless of what year you have. An ultrasonic cleaner would help. From the symptoms you described on how the bike ran I would suspect carbs. When you rebuilt them what kind of kits did you use and did you replace all the jets with the kits? If you did then you would be better off with Mikuni jets which are available from JetsRus. If you can post pictures of the carbs. When you went through the brakes did you completely disassemble the master cylinders and verify all the seals were good?

I will look into the carbs again. Don't remember the kits, but i do seem to remember jets being replaced. Only items not replaced were floats, emulsion tubes and diaphragms. I will try to get some pics of the carbs within the next few days. Not only did I disassemble and clean the front and rear MC, but i replaced all the seals. I also rebuilt front and rear calipers.

[DiverRay]

Did you keep the "old parts" when you rebuilt the carbs? If so, clean them up and put those back in to start. The needle and seat should be OK, but I have had problems with some K&L kits with them not sealing properly. The K&L Jets ARE sized wrong, and make trying to tune the bike a nightmare!

[jdub89]

Did you keep the "old parts" when you rebuilt the carbs? If so, clean them up and put those back in to start. The needle and seat should be OK, but I have had problems with some K&L kits with them not sealing properly. The K&L Jets ARE sized wrong, and make trying to tune the bike a nightmare!

I believe I do have the old parts stored away but they mixed now and I've always read to keep the parts in the same carb. Is there a source to buy new Mikuni kits? I would hate to put those back in only to start over for a 3rd or 4th time. I'd like to just get this done right so I can enjoy it.

[DiverRay]

You should get new Mikuni needle/seats for the carbs. The old jets can be cleaned and re-used, and it does not matter what carb they came out of. Check the main jet size, and go up one with Mikuni only jets, for pipes you have. The stock pilot jets should work. Be SURE and put in the factory needle in the slide!! Aftermarket ones are almost impossible to tune correctly.

[jdub89]

You should get new Mikuni needle/seats for the carbs. The old jets can be cleaned and re-used, and it does not matter what carb they came out of. Check the main jet size, and go up one with Mikuni only jets, for pipes you have. The stock pilot jets should work. Be SURE and put in the factory needle in the slide!! Aftermarket ones are almost impossible to tune correctly.

Just to make sure I understand...I should buy Mikuni needles/seats(you mean the float needle, right?) and Mikuni main jets(up one size from current) then reuse stock pilot jets? While apart I should clean the hell out of the carb bodies, adjust floats upon reinstall, reinstall the slide needles that were previously replaced, and install the new needles/seats, stock pilot jets, and new main jets. Does all that sound correct? Also the bike does have a K&N filter. Should I go up yet another jet size(2 sizes total) for the extra airflow?

Apologies but I have minimal experience with carbs. I rebuilt carbs on an 86 Magna I used to own and this bike. I understand them for the most part, but I just want to make sure I understand completely.