Author Topic: Can't find engine vin? CB750 (Read 3715 times)

ChopSticks · « **on:** February 07, 2016, 03:04:06 PM »

Alright so I bought a non running 1974 CB750 last year, at time of purchased I was able to match the frame with the title, but I couldn't find the engine VIN for the life of me. Recently I took off the carb and air box and finally found the VIN CB750E-3113834 but I can't match it up at all from the serial directory link below. The frame does match though. any ideas?

http://www.sohc4.net/cb750k-serial-numbers/

MoMo · « **Reply #1 on:** February 07, 2016, 03:07:56 PM »

check this source http://www.hondachopper.com/engine/engine_mods/modifications.html

ChopSticks · « **Reply #2 on:** February 07, 2016, 03:11:35 PM »

based on that it looks like a '78 F3? how screwed am I if I've been ordering parts for a K4?

MoMo · « **Reply #3 on:** February 07, 2016, 03:17:55 PM »

Depends on what parts you've ordered. One question, does the rear wheel sprocket line up with the front? I assume it is a non-runner?

ChopSticks · « **Reply #4 on:** February 07, 2016, 03:26:17 PM »

Just ordered new carb and air filter boots and a whole alloyboltz allen socket bolt set

well the PO bought it running, then it stopped then I got it. and after a couple weeks I got it to run again but wasn't perfect. idle was everywhere and choppy that's when I found the crap boots that I am just not replacing

MoMo · « **Reply #5 on:** February 07, 2016, 03:31:03 PM »

Which carbs are on the bike? newer K7/8 style or older non-accelerator version? boots could be different

ChopSticks · « **Reply #6 on:** February 07, 2016, 03:38:16 PM »

http://www.cb750carbs.com/details.html

Based on this reference, I def have a earlier K carb, do I need the F carbs for it to run properly?

754 · « **Reply #7 on:** February 07, 2016, 06:41:14 PM »

Roundtop or coffin top carbs?

ChopSticks · « **Reply #8 on:** February 07, 2016, 06:58:03 PM »

No idea what coffin top is but they're exactly the same as the k1-k6 in that link with the rubber dust top thingies

seanbarney41 · « **Reply #9 on:** February 07, 2016, 07:16:36 PM »

Quote from: ChopSticks on February 07, 2016, 03:38:16 PM

http://www.cb750carbs.com/details.html

Based on this reference, I def have a earlier K carb, do I need the F carbs for it to run properly?

absolutely not, and imo, the roundtops are just plain better. I have had roundtops on my F3 for about 8000 miles now.

ChopSticks · « **Reply #10 on:** February 07, 2016, 07:23:11 PM »

Whew

do you know if the boots that I ordered for the k4 will fit? Also anything else I need to be aware of from the differences?

seanbarney41 · « **Reply #11 on:** February 07, 2016, 07:33:52 PM »

the boots should fit, although they might be a tight squeeze...lots of lube and a little heat from heat gun will really help. The boots I use are old and stretched out. What year is your frame and tank? You should post some pics. Its hard for me to think of all the changes required because I have spares from all years that I can just grab and make stuff work.

ChopSticks · « **Reply #12 on:** February 07, 2016, 08:11:41 PM »

My frame is a k4 and the tank looks from that era also it's orange specle.. I'm not home night now but I'll post once I get home.. What changed on the boots? I might still be able to cancel the order since they had to order them, but the site doesn't have the F boots available

Jerry Rxman Griffin aka MuthaF'er · « **Reply #13 on:** February 07, 2016, 08:22:02 PM »

Boots, does the head have 410 on top fin intake side? If so the intake fitting is larger.

ChopSticks · « **Reply #14 on:** February 07, 2016, 08:24:35 PM »

Any pic reference? I can check right now

seanbarney41 · « **Reply #15 on:** February 07, 2016, 08:31:30 PM »

77'/78' both f and k carb boots are a totally different shape than earlier boots for roundtops. F2/3 (77/78) boots will not work for you anyway unless you have the coffin top/Keihin PD41 carbs. What I can't remember right now is if the F3 intake spigot is bigger diameter than K0-K6...whether it is or not the K0-K6 boots can be made to fit. I have them on my F3.

Oops, I see Jerry has answered this question...what you can do is grind the inside diameter of your K0-K6 boots enough for them to fit the larger spigots. That must have been done to mine by a previous owner.

ChopSticks · « **Reply #16 on:** February 07, 2016, 08:41:54 PM »

I guess what's better, to keep my k0-k6 carbs and try to fit the k0/k6 boots? or look for a set of correct carbs and correct boots?

If the better choice is the former, would I need to get different jets or set the needles different to properly tune with the F engine?

seanbarney41 · « **Reply #17 on:** February 07, 2016, 09:14:27 PM »

I really don't think it will be very hard to fit the k0-k6 boots...as said before, I think the f3 carbs are overly complex with accelerator pumps and a really messed up choke mechanism and suck anyway and new boots for them are rare and expensive.
I dont know what my needle position is, but I run 115 mains, 40 idles, air screws 7/8 out...k&n filter in the stock airbox and a Jardine 4 into 1 with a loud megaphone

754 · « **Reply #18 on:** February 07, 2016, 11:36:34 PM »

Does your exhaust have two bolts or nuts holding pipe on or just a clamp with bolt underneath ?

ChopSticks · « **Reply #19 on:** February 08, 2016, 05:58:15 AM »

uploading for ref will reply once I get to work

ChopSticks · « **Reply #20 on:** February 08, 2016, 10:37:45 AM »

Alright I think I'll just keep the same set up and the new boots will somehow fit, since it's probably the cheaper route instead of trying to find a whole new rack of carbs. I just initially thought the engine needed a specific set for it to run properly

Not exactly sure about the exhaust the pic I uploaded above is the best I got they currently have 2 2into1 exhausts. Could you give me a pic reference for the two bolts or nuts or clamp set up? Since I live in an apt the bike is readily available until days I work on it, so just wanna make sure I know exactly what to look for

I tried googling the 410 stamp but couldn't find it anywhere so if someone has a pic of that would be great

flybox1 · « **Reply #21 on:** February 08, 2016, 10:51:06 AM »

Bottom right of photo, just below the cam chain tunnel.
Your pistons will also be stamped 401 near the wrist pin hole

Don R · « **Reply #22 on:** February 08, 2016, 11:09:58 AM »

At the head/header connection it uses two studs and nuts tightening a finned flange OR there's a flange with countersunk phillips type bolts on the engine then the finned pipe flanges clamp over it with a single pinch bolt. The latter is early style.
Some headers use no finned flange, just plates on the pipe and studs/nuts.

seanbarney41 · « **Reply #23 on:** February 08, 2016, 01:59:38 PM »

...not sure why you would worry about the exhaust clamps, as either style can be used on any cb750 engine...

754 · « **Reply #24 on:** February 08, 2016, 02:57:10 PM »

the reason i asked about exhaust , is to answer how screwed am i, if i order parts for a K4...
sucks to order an exhaust new the find out you have to source whole new mounting hardware..

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Author Topic: Can't find engine vin? CB750 (Read 3715 times)