Advice required on how to strip and clean bank of vb52 carburetors .

[Rampton]

Hi to all, I have a 1981 cb750 Dohc, with help from members I have been trying to get her running. So far charging system sorted compression test 130 average, valve clearances done. Pick up coils and plugs changed. Had carbs cleaned (sonic) and I have removed carbs and changed jets needle valves float valves mixture set at 1 3/4 turns out.put a colour tune on each cylinder 1&2 bright blue 3&4 only get colour when I increase revs then bright blue. Been advised by two brilliantly helpful members that the idle side of the carbs are at fault and to remove the carbs, split them down and clean and clean and clean the passage ways. The idle jets on this bank are pressed in. I am hoping there is someone out there who can advice me of how to split the bank of carbs and where to clean. I have got a E guitar string. So I've been a busy boy today finished off the valve clearances and removed the carbs.(posting some pics). Would greatly appreciate some good advice thankyou. 

 

[Rampton]

I have now downloaded the www.cb750.com/publicdocs/seanG/Hondacarb_manual_revG.pdf. and it is very instructive. I am wondering is there any videos out there showing how to clean the idle circuits with the "E" guitar string?, this would be most helpful.

 

[Rampton]

Hi to all,I have read that the VB carbs- pressed in idle jets can be removed, mine are the idle jets under the rubber plugs VB 52A. Has anyone removed them using an EZ out, help would be appreciated.

 

[Rampton]

Ok removed all 4 idle jets from my vb52A carbs used a 1.4mm easy out was a bit nervous, but was pretty easy. Cleaned with carb cleaner guitar string and compressed air. New jets pressed in. Ready to re-install the bank of carbs tomorrow.

 

[Rampton]

Re-installed carbs all mixture screws set @2 turns out #1,2,4 headers hot #3 warm. Put colour tune on #3 getting good spark but shows rich at idle(orange flame) open throttle and shows bright blue. Will re-sync carbs tomorrow, then lost if that doesn't work. Spayed wd40 around new boots both sets no increase in rpm. Tick over won't go under 1300 black knob free from stop so no more adjustment there. Anyone got any ideas or solved same problem. I have read pages and pages but no definite fix to this problem. Thanks for reading

 

[Rampton]

Oh dear not getting much help here, but will keep trying

 

[MickMick]

Oh dear not getting much help here, but will keep trying

I have a similar issue on 2 but as it is running smoothly enough, I chose to leave it and ride it this season. Will look to resync over winter maybe or in the spring as not many riding days left for me mate.

 

[Rampton]

Yep thanks going to strip them out and have one last go at cleaning the idle circuits if that doesn't work don't know what to do?!! Thanks for the advice. Had this bike two years and haven't had a proper ride yet would be nice to do so.

 

[dirtdigger]

Its been said many times the stock carbs are junk and almost impossible to get totally clean and running right. Dropping them in the scrap bin and biting the bullet and buying some aftermarket carbs is the best solution. Nobody likes to hear it but the stock carbs are junk

 

[Rampton]

Thanks for that, what carbs do you recommend? and what size ( 30 or 34s)? I read you recommend 4 carbs not 2

 

[dirtdigger]

4 cylinder bikes run best with 4 carbs.... you will lose overall power with the twin carb setups. Keihin CR carbs or Mikuni RS carbs. Dynoman.net says 29mm for the CR. Cyclexchange.net has Mikunis, I would email them for there input, I am guessing they with say the RS 34mm. Carb sizing depends on engine size, any performance modifications in engine, exhaust system, intended use.

 

[Rampton]

Thanks dirtdigger for the response, I agree with you about these stock carbs I'm having a mare trying to get them to operate when everything on my bike is stock no mods all OEM parts. Like the sound of a new bank of carbs, will make some inquiries. Thanks again for the help