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GS 550 Jetting

  • Thread starter Thread starter Anonymous
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Anonymous

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Hi to all and greetings from a new forum member from Scotland.

Ok here is my problem. I have a 1981 GS 550L with Mikuni CV Carbs. I have fitted a set of S & B Freeflow type air filters and as expected it does not like them due to the huge increase in air flow. It idles ok ( as expected ) but it does not like to rev beyond 3OOO and when I open it up it just dies. Now I know you can fit a dynojet kit to solve this but they are really expensive as I only fitted the filters for looks not performance.

Is there any quick mods I can do to help it run better or have I made a big mistake in going down this road.

I bought this bike as a cheap project - now theres a contradiction in terms!!

Look forward to the replies.

Regards
 
Technicly, you need to tune the carbs to your setup which is now changed due to increased airflow. You should be able to get away with just swapping out the main jets with ones a couple sizes bigger, exactly what size needed will be specific to your bike and may take some expierimentation. You can probably get the jets at any shop that sells parts for mikuni carbs (atv/dirtbike shops etc) for af few bucks a piece.
 
Thanks for that. I may wish to try this route. From my manaul it says that the main jet size is 92.5 ( I have BS 32 SS Mikunis )

What would be the size I would need to get if I have to go 2 sizes up.

PS I Broke the old air box removing it so that option is out at the moment.
 
you can try increaseing the jets but the jet kits come with more then just main jets they have adjustable needles and a piliot air restrictors too. you can give just bigger jets a try, my kit for the 550 came with 2 sizes 150's and 155's i would try the 150's also the jet screws had a smaller out diameter head then then the oem jets i think that, that also effects the fuel flow.


ryan
 
you may have to raise the needle a notch...

run the bike good and warm, then open the throttle and let it die like you said. pull the plugs, and check if they're white (lean) or black and wet (rich). this will help you determine what is going on when you gas it.

~Adam
 
runnersleep said:
Thanks for that. I may wish to try this route. From my manaul it says that the main jet size is 92.5 ( I have BS 32 SS Mikunis )

What would be the size I would need to get if I have to go 2 sizes up.

PS I Broke the old air box removing it so that option is out at the moment.
Click to expand...
You are not getting the full performance from your pods unless you also install a free flowing exhaust. However, you did say you're only after the looks of the pods. I think you should repair or replace the stock air box.
If you insist on keeping the pods, you WILL have to buy a jet kit. Your needles are not adjustable and there is no way your bike will run right with your stock needles. Your bike will run very lean and you risk overheating and damage to pistons, valves, etc. When riding, you are most often using the needle jet circuit. A larger main will only help when riding at 3/4 throttle and above.
Buy a jet kit, such as Dynojet, or go back to the stock air box.
Also, jetting can be very frustrating, especially if you've never done it before. If you don't have the patience or ability and don't want a mechanic or ? to jet it, then go back to stock.
 
Thanks for advice Keith. I shall consider what has been said and decide a way forward although I do like a challenge and may go for a jetting kit.

Will keep you posted on the outcome.

Thanks

Martin
 
runnersleep said:
Thanks for advice Keith. I shall consider what has been said and decide a way forward although I do like a challenge and may go for a jetting kit.

Will keep you posted on the outcome.

Thanks

Martin
Click to expand...
OK. Let us know if you need help with the jetting.
By the way, a vacuum tool is very important when tuning/jetting carbs.
You mentioned a concern over expenses in staying with the pods and re-jetting with a jet kit. So add the tool to your list. It's worth it.
 
Hi All,

Just thought I would let you know - mission accomplished - I decided to go for the Dynojet kit stage 3 and believe it or not I got it from Dynoman in Austin Texas. It arrived in 6 days and I must say the service was excellent( also half what I would pay here in the uk). I fitted the 150 mains and set it up as per the instructions ie drilled the slides and fitted the needles at No. 3 setting. It fired up first time and I am dead chuffed!! Perhaps a little adjustment later but I would say it is running 9/10

I bought this bike back in june for ?400 uk and have spent about the same again on it. I have fitted a katana BSM exhaust which I got for a bargain here in the UK and have modified the tail end a bit and put on some small blinkers. Also its had a cuple of oil changes and the brake pistons replaced.

I now like what I have done to the bike and am now looking forward to enjopying riding it although winter has arrived here in Scotland so opportunities will be limited.

Thanks for your advice and help and I will post a pic as soon as.

Regards

Martin
 
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