750 Seca to run with 650 Carbs?

I have a xj 750 with 650 /32 mm. carbs that are thoroughly rebuilt with 124 main jets. Got the carbs synchronized the best I could. However, still won't idle and have to keep high revs to keep running. Question is, can 32mm. carbs run a 750cc. block?. The manual shows 34mm. for 750's.

 

Pretty sure the 5G2 750 engine is using the same carbs as the 4H7 650 engine, bsc32 Hitachi with different jetting.

I know there are some 750 engines that used mikuni carbs... And kinda looks like xj900s cosmetically.

The 33F 853 uses bs34 while the 58l 891 uses bs35 mikuni, they are both Xj900 versions.

What is your engine number prefix?

 

The 650 and 750 use the same 32mm Hitachi carb but with different jetting. I don't have that information off hand but it's available here somewhere. The 700 Maxim I believe used a 33mm Hitachi body if I recall.

 

It can run on either engine as just jetting is different. Did you replace the throttle shaft seals? If the seals were replaced were they installed the correct way around? Is the choke circuit fully closing? Are the inlet boots sealed properly and did you change the jet sizes......

It sounds like a tuning issue...

 

The jet needles are also different for the 750 than for the 650. Those will need to be swapped into the 650 carbs

Are the air jets in the correct places, and not where the service manuals show them?
There are several errors in the manuals. Small, but important errors.



It's also really important to know which 750 you have. There are three basic differences when it comes to which carbs to use. If you have a 81-83 750 then it's the same carbs as the 650 and it doesn't matter if it's a Maxim or Seca.

It's customary to list the year and model in your signature so it always shows up when you post a question (mine is in red). It's also helpful to keep everything about one bike in a single thread so we can keep track of the history of the project and not miss things that may be contributing to a problem.

 

1981-83 XJ750 Seca and Maxim (including 1984 XJ750 Maxim in Canada and XJ750 UK/Euro models) use the HSC32 series carbs.

1984 XJ750RL Seca (Canada and Australia only) use the HSC33 series carbs (same as the XJ700 air-cooled models and a few others).

 

http://xjbikes.wikidot.com/carb-specs

 

That's great!
And my memory is shite obviously as my post was full of misinformation.

 

The eng. # is G N8026054. What is th bs35numbers?. I have a yam. Factor manual to look up anything if needed.

 

The BS35 number is the Mikuni carb model.

 

Hello Mezzmo,

Where are the throttle shaft seals?. I will do that next.

Thanks,

 

Here is a link to "The Church of Clean"
https://xjbikes.com/forums/threads/in-the-church-of-clean.14692/
@SSecacsm89, reading through that thread is great and will show you have far you will have to break down the carbs to get to the "throttle Seals". Take your time, slow and steady and use good fitting tools.

 

Does anyone know where to locate the carb. rack numbers?.

 

650's and 750's use the same carburetors, the differences are in the jet sizes. The jet sizes are stamped on the individual jets. The carbs have to be removed and the float bowls off to be able to see what is stamped on the jets. 650's will run well with 750 jetted carbs and vice versa, just not optimally..

 

On Hitachi carbs, the rack ID is ink-stamped onto the (exterior) bottom of the bowl, in the large flat area. If carbs have been cleaned, dipped, cleaned with a strong solvent, etc. it is likely that the markings are gone.

Mikuni carbs have ink-stamped ID numbers on the side of one of the outer (usually the #1 carb body), right below the carb hat.