Topic: cb750k4. now running

[poogerwrestlin]

Hey guys and gals,

This is my first forum post about my first "restore"on my first and only motorcycle. I was given this bike by a relative that had a bad habit of riding drunk. When I got it, he said it needed work and that I should sell it for $500. I saw the potential and could not let it go.  The wiring was a mess. Duplicated wires, plugs carbon or oil fouled, carbs in desperate need of rebuild and sync, rear tire bad, multiple oil leaks, broken push throttle cable, and intermittent loss of 2 cylinders.  I have spent the last year learning as I go. It is now fairly reliable, but still needs more work. Main problem I have is that it fouls 2 plugs every 50 miles. Those two plugs run off of the same coil and always seem to fail ~20 miles before the other 2. Unknown if carbon or oil fouled. I got a set of aftermarket carbs for free and had a local shop jet and sync them, but it still keeps killing plugs.  If it is running rich, then it is only slightly rich. Any recommendations?

[calj737]

The fact that you keep fouling plugs, whether 20 miles sooner than the other set, is a clear indication of fuel related issues.

Your picture shows CR carbs and velocity stacks. Who set these up for you? That is a pretty aggressive setup for an otherwise stock engine. Are they 29s or 26s? They are great carbs but designed for high rpm riding and can provide a great deal of fuel for that requirement.

Do you know the configuration used by the "shop" when they were setup?

[MoMo]

Put the stock air box back on is my suggestion.
What are aftermarket carbs?

and welcome...Larry

[poogerwrestlin]

They are the cr29 race carbs. I got them for free from a friend of mine that bought a pallet of them for $1200 at auction. I know the pilot jets were reduced in size and that they were synced. Another thing that may be a factor is that I need new exhaust.  A previous owner hacked away about half of one of the baffles damaging the pipes before the megaphone. I got the carbs synced without the pipes because of this.  Trying to find stainless pipes that look stock (pic attached).  so far as the air box, it will not fit these carbs even without the stacks. The stacks came with the carbs. Filters for the stacks cost about $70 a piece. Since I am strictly using these carbs just until I get the stock ones the way I want, I do not want to pour money into them. The original carbs had jet sizes reduced because of how rich it was running and fouling plugs in a similar fashion as with the new carbs.

Sounds like the recommendation is fix the original carbs and go from there... 

I will post pics of the plugs when I pull them. Pics of the exhaust I may buy is #1 pic of bike today is #2

[poogerwrestlin]

Oh and no idea why the camera time stamp is from 2013. photo was taken today...  ording rebuild kits for the carbs now with an assortment of jets. Carbs have already been ultrasonic cleaned, 2 floats replaced, and one float pin replaced. Work over past couple months :New wiring harness installed, new coils, points, capaciters, chain guard, and handle grips.

[calj737]

Keep the CR-29 carbs, but ditch the velocity stacks and go with pods. Don't misunderstand, they're great carbs, but you'll need to spend some time tuning them in just right. And until you resolve your exhaust, it'll be harder to do.

Then again, you could probably sell those carbs for much more than a fully rebuilt stock set with an airbox. Your choice in the direction you wish to follow.

[SOHC4 Cafe Racer Fan]

Keep the CR-29 carbs, but ditch the velocity stacks and go with pods. Don't misunderstand, they're great carbs, but you'll need to spend some time tuning them in just right. And until you resolve your exhaust, it'll be harder to do.

Then again, you could probably sell those carbs for much more than a fully rebuilt stock set with an airbox. Your choice in the direction you wish to follow.

Both solid suggestions.  I would keep the CR29s if the engine has or is going to get a big bore kit and possibly a cam and port job.  That will make the most of the carburetors.  If your engine is going to remain stock, I agree with Cal that you could sell them to fund your airbox and stock carb purchase.