max 5000 rpm

1980 xj 650 uk 4ko,have written on here last week with regards to running like a bag of shite guess what? it still is, new manifold rubbers, new diaphrams, several cleanouts, blowtrhoughs galore, the thing still runs like crap. up to 5000rpm a bit slow ,but then nothing for a couple weeks dosent change no matter how much throttle you give it,when its stood and revved goes clear past 7000rpm,but under load have touble getting it past 5000rpm,could it possibly be the coils packing up under load?,i dont really know,ingnition control unit? has any body out there looked at the haynes book of lies where it shows the view of the pilot jet and main jet looking down the diaphraghm bore, is this wrong (a= pilot jet) (b=main jet)im confused :cry: :x

 

Ok Haynes manual page 120 photo 7.2 In the center of the carb body are two posts. The tall one is the main fuel jet and the short one the pilot fuel jet. The jets being the brass fittings that screw into the posts.
Page 128 photo 12.3 This is the pilot mixture screw. did you remove them when you cleaned your carbs? If so they need to be set with the colortune plug which is referenced on the site many times. If this has been done then proceed directly to changing out the TCI.
If the screws were not removed then the carbs are not clean. Sorry to say that but I have been there too dude.
If they were removed and not colortuned because you don't have a colortune plug then I would suggest gently screwing them in until they stop being very careful as they stop because this is their fuel seat that stops them and you could damage the seat or the screw. The screw has a very fine needle point at the end which is very delicate. Once seated then back them all out 2.5 full rotations. Crank engine and see if there is any difference.
If this was the method you used to replace the screws then I suggest backing them out one half turn "one at a time" with the engine running and listening for an idle improvement. Then checking with a short ride.
Also Haynes manual page 123 photo 7.9b The main and pilot air jets are backwards. If you installed them this way reverse them. If you didn't remove them for cleaning..smart boy...they don't need to be removed to clean the carbs. Let me know anything else that could help or you need help with.

 

I just went back and found your other topic and read the posts. Most likely it is the TCI. If it is/was running smooth below 5k rpm then forget about the carbs except for that one post where it ran worse after getting fuel. No inline fuel filter could have let moe trash in the carbs. I still am betting on the TCI. Mine did the same thing right after a major carb rebuild. I was riding with all well and one morning n the way to work it ran like crap at about 4700 RPM. Below that it was smooth. Eventually it ran rough even at slow speeds. On a whim I changed out the TCI and it ran like a raped ape!

 

Don't do anything until you pull your carb drain screws and collect the drainage onto a clean pad of kleenex tissues ... examine that which drains out for particulate ... or, sediment looking like brown baby powder.

Pull drain screws.
Carbs drain: Yes / No
Yes: Check drainage for particulate.
No: Clean carbs.

Particulate: Yes. Clean carbs.
No: Check coils.

No particulate -- check coils for break-down.
Primary - the small wires -- 2.5 ohms + / -- 10%
Secondarys -- the spark plug leads -- 11,000 ohms (min)

Coils OK? Check "pick-up" coils to specs.
Clean pick-ups with spray electronic parts cleaner.
Clean connections on "the box" with electronic parts cleaner or contact renew.

Check fuse panel clips and leads for corrosion and possible loss of ability to hold fuse tight ... sympton of pending fuse panel failure.

 

cheers to all for your feedback,unfortunatley have run out of time to fix it now so will be going to the bulldog on a pink virago bit of a change from the black xj,carbs came to pieces completly,on page 123 it shows big hole at the top smaller hole on the bottom but the wording tells a different story,next line of enquiry will be the tci uit and coils thanks once again for all your input archie

 

http://www.slygrin.net/xj750/html/body_carbs.html
Try this site for help while cleaning your carbs. I also PM'd you a carb cleaning guide.