CB750 DOHC starter pack? - what do i need before i start

Hi guys,
Been lurking and reading all the great builds on here so I picked up a DOHC CB750 and now want to get it running well, to start.
The seller had it running, but wouldn't hold idle .... It would also cut out when revved above 4,000rpm

I did notice he was running it with one of the air box covers off, and i've read too much air can be a problem, so i'll be sure to have the cover back on.

My question is, what parts should I buy and have on hand before I start tinkering with it?
It came with a second set of carbs so that could be useful to diagnostics or spare parts.

- New plugs?
- Any of the ignition parts?
- new carb-to-head rubber boots?

Thank you!

Year and which model? There are sites that specialize on CB750s and some that specialize on the F or C bikes. Plugs, yes. Hold off on other parts just now. The first thing is the Honda service manual and at least a link to the parts fiche (I usually use Southern Powersports http://parts.southernhonda.com for that). Many aftermarket suppliers on the 'net. Many parts no longer available, too. Ebay is your friend there. Next thing is check and correct valve clearance (Honda sez .002 - .004", experts say .004 - .006?), then check compression. You have the right idea of getting it running well first, and avoiding pods. Make sure you have the air filter and spring under it too. Many folks have worked furriously to clean these carbs, only to reinstall with dirty gas tanks and no fuel line filter. There is an excellent carb cleaning manual from SeanG on one of the sites - pictures and all. Then, before riding fix the brakes and update the tires if needed. Many older bikes that have been sitting have tires old enough to vote!

Sorry ... i thought i had included that.

1983 CB750SC - Nighthawk

pidjones said:

Year and which model? There are sites that specialize on CB750s and some that specialize on the F or C bikes. Plugs, yes. Hold off on other parts just now. The first thing is the Honda service manual and at least a link to the parts fiche (I usually use Southern Powersports http://parts.southernhonda.com for that). Many aftermarket suppliers on the 'net. Many parts no longer available, too. Ebay is your friend there. Next thing is check and correct valve clearance (Honda sez .002 - .004", experts say .004 - .006?), then check compression. You have the right idea of getting it running well first, and avoiding pods. Make sure you have the air filter and spring under it too. Many folks have worked furriously to clean these carbs, only to reinstall with dirty gas tanks and no fuel line filter. There is an excellent carb cleaning manual from SeanG on one of the sites - pictures and all. Then, before riding fix the brakes and update the tires if needed. Many older bikes that have been sitting have tires old enough to vote!

Click to expand...

Thank you for the advice! I appreciate it!

For valves, i have been confused ... do i check, then order the proper shims as needed, or do most people prefer to buy a full shim kit to have on hand?

Yes, compression, i have even found a compression gauge, i just need to find the right fitting. I guess i'll do that once i pull the spark plug out and see what threads i need for it.

I will look for the carb cleaning manual. But, do i just assume they are dirty, or is there a way to diagnose dirty carbs right off the bat? Thanks so much!

Wait until you have measured the valve clearance, and just get the shims that you need. There is a special tool (Motion Pro makes one, you can buy it on Amazon or ebsy) for removing shims - don't rotate with shims removed! I bought a bunch of shims from a guy getting out of CBs for very little on ebay. 25mm diameter is also used in some other bikes and even some Toyota cars. There are spreadsheets to help cakculate needed shims and some even direct swapping to minimizeshim purchases. The adapter to fit the plug holes came with my Harbor Freight compression gauge, and it has worked well for me but others have had bad luck with it.

These links will help (may need to join the sites, but they are free):

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=5

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=13611

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=11019

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=12173

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=17825

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=13994

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=5408

http://www.cb750.com/forums/21-The-DOHC-Garage-(1979-1983)

Thanks for the reading material!

I'll register on there as well and have a read. Interesting that cb750c forum didn't show up in any of my google searches .... just cb750.com, sohc4 and this one. Maybe i just didn't notice. Thanks!