Bimota SB3 help

[Guest]

Hey Fellas,

I have a 1980 Bimota SB3 which was built as from a GS1000 (pics elsewhere on this site in the gallery under 1980). I've had some running issues where she does not want to pull beyond 5500 RPM. Occasionally she will get a little motivation at that speed but it never lasts more than a few seconds. I have thoroughly gone through the carbs and they are good. I replaced the previous Dyna S ignition as it was not getting spark to two of the cylinders and did new wires, caps and plugs at the same time. Of course the bike sat for extended periods during these various changes to the tune of several years at a time making me very quick with the carbs. So before I toss new Dyna coils on the girl I want to verify some information. i would rather learn something instead of tossing parts at the issue till the problem is solved. I want this setup running right before I toss the Keihin CR31 smooth bores on which I have sitting on the shelf.

1. My engine number is GS1000-135676 . What year GS1000 is this and which model?

2. I'm using NGK B8ES plugs with .030 gap. Are these correct?

3. Do I need resistor plug caps? If so who sells the proper caps and wires?

Thanks a bunch for any help.

[ShadowFocus603]

Have you checked the o-rings between the intake boot and head? When you went through the carbs did you replace the o-rings? www.cycleorings.com is a great source for both, as well as stainless steel fasteners for the boots. Are the intake boots themselves in good condition? IE no cracks tears etc. What air filter are you running? If stock GS1000 airbox are the boots from carb to box soft and pliable? Did you seal airbox side covers? Most people here use foam weatherstripping in the 1/4 to 1/2" variety. Seal the filter to its opening with same. By now I am assuming you get the idea that I am betting you have an air leak causing a lean condition. The bike starves for fuel due to air being introduced where it shouldn't be causing an excessively lean condition. Riding the bike as is will eventually cause damage from overheating. http://www.z1enterprises.com/ItemDet...item=TU38-1006 The spark plug boots I use for all my bikes at the best price. If you need something besides the angled like those they have them as well. http://www.z1enterprises.com/ShopByC...01010405030807 All the ignition stuff for your engine, assuming it's a 1980 or newer. Easy way to tell is if it has CV style carbs vs the older VM style.

[rapidray]

Start with closing the plug gap down to .020. Call me at 714--356-784 five & I will be glad to help you out.
Ray.

[Fjbj40]

The plug gap, as Ray said, needs to be about .020 especially with the Dyna ignition and more importantly with the Dyna coils.

[texascbr]

Thanks for the responses. I pulled a plug last night (in a rush so just one) to quickly verify which ones were installed and check the cap and wire. Will install a new set of plugs this evening or tomorrow with new NGK XD05FP caps and fresh copper wires.

The plug I pulled indicated a rich condition but that is likely due to letting the bike run multiple heat cycles to include choke while sitting in the garage. The last ride before parking was ~18 miles Saturday and she was not started since.

The O-rings and boots were replaced recently but I will check for air leaks if the new parts above do not make a difference and regardless next time the seat section is pulled. The bike uses K&N pod filters with a special Bimota exhaust. She was running fine with this configuration for the prior 20 years when running before the issues started.

Ray I may call later after I check the obvious items mentioned.

Thanks a bunch for the hints.

[1980GS1000E]

I would check for fuel starvation as well.

[Big T]

Hmm

Which carbs do you have, the 78-79 VMs or the 80 BS?

Or does the Bimota have some aftermarket carbs? I'm assuming you have pod air filters on it?

Sitting for months will clog up your carbs in mere weeks

This sounds like a BS carb issue

[texascbr]

This may very well be a carb issue. When I pulled the plugs last night I noticed something odd. Cylinder 1 and 2 plugs look good to perhaps a tad rich while 3 and 4 looked very lean. Counting 1-4 going from left to right as if sitting on the bike. IF I am not mistaken 1-4 fire on one coil and 2-3 on another. So it would make no sense that a coil is bad.

I have rebuilt the petcock and tested her and flow seems great. When driving the bike last I even had the petcock set to prim to ensure flow which was also good when tested with the tank off the bike in the week before the ride. What I have not tested is the gas cap to see if it is venting properly. The fuel filter on the bike is giving great flow as demonstrated last week when I put the carbs on and fired her up and a float stuck causing gas to quickly puddle under the bike. (float height on all 4 carbs is set per the manual).

Not sure which carbs are on the bike as this was built from a kit in the early 80's I did post the engine number below hoping to shine some light on what I do have.

Thanks for the help,
Chris

[GregT]

What little can be seen of the carbs in the gallery pics suggests VM's to me. Slide type carbs VS butterfly valve CV carbs. Some of your probs could well be poor synchronisation of the slides but the VM's are also very prone to blocking of the internal passages when they sit for long periods. With pods, I've found more than once that the air corrector passages seem more prone to blocking too which again sounds very like what you're getting.

[Big T]

Greg T

Yeah, I was thinking that sitting on the sidestand that long may preset issues for the uphill carbs,, 3+4

The pods may be the issue as you noted. Good pods? like K+N or cheap pods?

[texascbr]

The pods are new K&N. About to pull the bodywork again and verify I have good electrical connections going to the coils.

The carbs should be good as they were completely gone through before the last test and I synced them after installing. As two plugs are rich and two are lean it makes me feel comfortable dismissing a fuel cap or flow issue.

[Big T]

The carbs may have been good years ago but have clogged up now

How long ago did you clean them?

The serial numbers are meaning less for a kit bike

[texascbr]

The carbs were cleaned and checked before putting on the bike a week before the ride mentioned in the last test. Agreed, things will change if left alone regardless of fuel or no fuel in the carbs. During my testing I've gotten quite good at pulling the carbs and do so before trying a new test if she has sat for more than a couple months. I have also run them by the shop and had a second set of eyes verify.

The engine number is listed to try and discover information about the donor bike and the parts I'm working with.

[texascbr]

It's been some time but I wanted to add updates.

1. Upgraded to Keihin CR31 smoothbores with 120 main, 70 pilot and the needle jet is raised to the highest setting. These have pod filters.
2. New dyna coils
3. New plugs properly gapped, and wires from Dyna
4. Electrical connections cleaned
5. New Battery
6. Gas cap cleaned and checked
7. Fresh inline fuel filter which flows very well
8. Bike is run with petcock on prime when running (no vacuum on new carbs)

The bike on an initial run ran amazing but I did have a stumble once or twice that felt like the bike was missing. The second time I rode her she had a resistance at the same point of 5500-6000rpm but appeared a bit more compliant.

At this point connections have been cleaned. Plugs and wires replaced with recommended .20 gap. New Dyna S ignition installed and timing verified. Coils and Battery are new. The only thing remaining is the CDI box but I was under the impression it would either work or not. The gas cap is venting fine.

She's running better but every now and then she hesitates or stumbles. Any ideas? Replace CDI box?

[JamesWhut?]

Sounds like your mid to upper main jetting is off (over rich) or your sync is off. Yes, CDIs usually are good or they are bad. You can try cleaning the contacts on the connectors. Sometimes that helps.

Cool bike. Do you have a replacement GS1000 motor or the original Bimota one? They were not the same. The SBs are not a :kit bike" nor are the motors "donors". They are factory built, Bimota just sources engines from other factories and concentrates on advanced chassis and groovie bodywork.