Carb Question...Can't get it right

[MikeyZ]

Hey guys..

Im trying to get a 1990 Katana 750 back on the road.

I cleaned the carbs, put new plugs in it, cleaned the air filter, fresh fuel lines, fresh gas. The bike has a VH 4-1 exhaust.

The bike will start and run and idle.

However when I am riding it down the street and I pull the clutch in to come to a stop the bike will stall. It will start right back up after but it is a pain in the ass. I could be riding, pull the clutch in in the middle of the street, the bike will die and then i will just have to release the clutch to bumpstart it back to life.

Also, not sure if they are related but the bike lacks serious power. It will move, but very sluggishly. (I think this is the exhaust without a proper jet kit)

[Rossco]

Check your vacuum lines. That bike has CV carbs that rely on vacuum pressure.

[MikeyZ]

Check your vacuum lines. That bike has CV carbs that rely on vacuum pressure.

Yea it has 1 vaccum line from carb 4 to the petcock. I have it hooked up and it is tight fitting but I never put any clamps on it. Think that could do it?

[Speed Demon 828]

Make sure the carbs are 100% in the intake boots. Also the stock pilot jets may be way too small for that exhaust system and you may have to go up a couple sizes.

[Speed Demon 828]

just re read your post. It will definitely need new pilots and mains with that exhaust.

[Doc]

By "cleaned" the carbs what do you mean?

Did you take them apart and remove/clean the jets?

Is the idle speed adjusted correctly? All the boots sealed well?

[Sheppo]

Every thing that has been said is very good advice. I have owned one of those Also make sure the air cleaner is seated correctly, those boots are a pain in the a$$. Also are the intake boots cracked?

[MikeyZ]

By "cleaned" the carbs what do you mean?

Did you take them apart and remove/clean the jets?

Is the idle speed adjusted correctly? All the boots sealed well?

Fully broken down the carbs, Removed all rubber pieces, soaked every jet/ emulsion tube in carb cleaner over night. Ran some fishing line through the pilot jets. I didnt soak the whole carb body, but I did thoroughly clean it with q-tips and a lot of carb clean/ compressed air.
(I have cleaned Katana carbs before with success)

The idle speed is adjusted correctly, It WILL idle just sitting in the driveway, however just dies on the street after being revved for a little.

I think it might be the boots. I never fully checked these and one of them "rotated" in the airbox. I was told to seal them up with RTV? Think this will fix it? Does that make sense that it would idle in the driveway but die after being revved?

From Speed Demon:
"just re read your post. It will definitely need new pilots and mains with that exhaust"
I replaced the main jets with a size one bigger. And also shimmed the stock needles with washers. It seemed to help with the power a TINY bit, but the bkes still a pussy.

[Doc]

Sounds like you cleaned the carbs correctly

Can you make it repeat the issue when warm in your driveway?

It might just be running to lean.

[Speed Demon 828]

Katanas are notorious for tiny pilot jets. Go up a couple sizes.


With the lack of power you are going the right way with the main jets and needles. Todays fuel is so crappy that we are finding that we have to go much bigger than known jet sizes for common mods. i.e. pipes and air filters.

Also did you pull the(idle) mixture screws out and clean the passages? You might also have to back those out a 1/2 to full turn from where they are.

while you are there it would be a good idea to pull the spark plugs and see how they are burning.

[MikeyZ]

Katanas are notorious for tiny pilot jets. Go up a couple sizes.


With the lack of power you are going the right way with the main jets and needles. Todays fuel is so crappy that we are finding that we have to go much bigger than known jet sizes for common mods. i.e. pipes and air filters.

Also did you pull the(idle) mixture screws out and clean the passages? You might also have to back those out a 1/2 to full turn from where they are.

while you are there it would be a good idea to pull the spark plugs and see how they are burning.

The exhaust is in awful shape anyways between rust and dents. I think I am just going to get a stock one and hopefully it will fix some troubles.