Topic: Help! 76 CB750 Dies At 60mph! WTH??????

[dusterdude]

seaweb,im not going to re-read all these posts on this,so if myself or someone else already recommended this,please pardon my old ass.have you pulled the choke on a bit when riding at 60 mph.if you do and the bike picks up and runs properly then you are running lean for some reason be it jetting or lack of flow.let me know how that turns out.reason why i ask my bike kinda falls flat at 60 unless i give it some choke,and i know im lean,at least for the time being until i fix it.

[seaweb11]

I did not have a rpm issue.

Good luck.

[dusterdude]

seaweb,you still having issues?

[seaweb11]

No problems with the 750. Someone just opened up an old post. "wasn't my post".

I am having problems with the CL350 though.....
http://www.sohc4.us/forums/index.php?topic=4489.75

[dusterdude]

groovy

[endobendo]

Hey hacknslash, a while back you mentioned the bike has pods.  Check the numbers on your main jets to make sure they are larger than stock.  I believe the stock size is a #105 or 1.05mm.  To run pods you will need something like a #120 or #125. 

When I bought my bike the PO installed pods without rejetting and the bike would not rev above 4500 RPM, it would fall on its face.  I bought an airbox and K&N filter off ebay and will never go back to pods.  Sounds like your bike is lean to me.  Let us know what you find.

[seaweb11]

SiliconDoc
The post above says bigger jets....but still not big enough.
Go to 138s or 140s with the pods on your mains.

[dusterdude]

uh doc,where u is?

[tdogg1966]

At one point I was new to the sohc, also. I had the mechanical ability just no knowlege of what i was working on. Check this site out ...very helpful!!!

http://www.salocal.com/sohc/

[Hockers Choppers]

Hey Guys,
I just bought a 78 cb750f off ebay and am trying to get the jetting right also. It has an aftermarket 4-1 and I plan on putting pods on it. I live in KS about 2000ft. Are the 125 jets about right for me? Any other cheap hop up tricks? I'm into performance. I,ve rode Harleys for the last 20 years and just am tired of spending so much money on little performance. Thanks Jesse

[cd811]

welcome hocker...good people here...now your question just leads to other questions...why change jets?...what do your plugs look like?...is there a problem?...there is no standard for jets in these machines, so jet size will vary from engine set-up air filters, exhaust system, compression, ignition, and on and on, so more info is needed...some guys just throw jets in and get it right the first time and some (like me) are still fine tuning....welcome,enjoy and good luck

[Hockers Choppers]

It is stock as far as I know. The bike seems to just run out of power at around 7000rpm. It doesn't pop or anything, just seems like it should pull more. The plugs look ok, just a very light tan little on the lean side. I know all about the time it takes to fine tune a carb, I had a 77 iron head sportster years ago that I put a mikuni carb on and fought the jetting the entire time I owned that piece of crap!! Then an evo sporty with all the buell stuff in the engine (85 hp !! and $10,000 ) Same thing with a 88 Electra glide with a s&s carb cam pipes ign. etc. Then a 2003 ultra EFI with cam, pipe, race tuner, etc. the efi was a total pain in the pocket book Nice ride but way too much money! I could buy 30 of these Honda's for what I had it that bike and am having just as much fun! Just trying to get maximum performance. Thanks

[flatblack]

The bike seems to just run out of power at around 7000rpm. It doesn't pop or anything, just seems like it should pull more. The plugs look ok, just a very light tan little on the lean side.

What's it do when decelerating? If it chugs a bit, that would be the second indicator (plugs being the first) that it's too lean. Adjust the air screws in a 1/4 turn and try again.

HTH...

fb

[Hockers Choppers]

No chugging( till I get to the fridge in the shop ) runs fine untill wot. Cold blooded as hell. Maybe its all the power it has? Just seems like it should have more. I'm going to take the carbs off and clean them, put on the pods and start with a 125 jet and see what happens.

[scondon]

  Welcome to the site Hocker. Stock main jets for your bike are 105 and the engine should pull well at WOT with stock airbox/filter using this size jet. The 78 750F runs a tad lean with the stock jetting but not so much that I'd want to change it. I did find some benefit in richening the idle circuit by turning the fuel mixture screws out 1/2 turn from the stock setting of 1 3/4 turn. I think that anything over 110 mains would be too rich at WOT, 115 mains if your running pods. At least that was the case for me here at sea level.

[mrbreeze]

Hey Sean,I'm running 138's and thats where mine seems to be OK.Now at 2000 ft....Ithink I would go with 120-125's. That is if you are going to run pods. So where are your needles set or are these the newer 750's with no needle adjustments?Mine are at #4 from the top so they are the next step up from as lean as you can go.

[scondon]

Hey Sean,I'm running 138's and thats where mine seems to be OK.Now at 2000 ft....Ithink I would go with 120-125's. That is if you are going to run pods. So where are your needles set or are these the newer 750's with no needle adjustments?Mine are at #4 from the top so they are the next step up from as lean as you can go.

     MrBreeze, Glad to hear ya haven't melted in the Central Valley heat I haven't yet got a bike to run well at WOT with mains over 125-130. From the sound you made tearing out of the parking lot last month I'd guess you're running a pretty open exhaust in addition to pods?

   I've been all over the map with different carbs and setups these past few years. '73,'76,'78 model carbs, stock filter,K&N Filter,pods. K8 engine, F3 engine, 836 engine/hot cam/ported head, 73 topend/78 bottom end engine. Currently working with the 73 and 76 carbs on the 836. These carbs look almost identical, but the '76 set has clip in the middle(runs a bit rich) while the '73 set has clips 2nd from the bottom( 1 position richer) and run a little lean. I am thoroughly convinced that there is no quick answer that can be given for anything other than bone stock in perfect running condition. A good starting point is all I could hope for with mods.

    That said, I actually started my SOHC career on a bone stock F3 with a K8 engine in perfect running condition. Later on I got a bone stock F3 with original engine and pod filters. The F3 with K8 engine ran great with 105 mains even after I put a K&N in the airbox. The other F3 with original(black) motor and pods ran great but didn't pull as well at WOT, this bike was jetted with 120 mains. I pulled the plugs and since they looked a bit light I jetted up to 125 and WOT got worse. Around this time SamCR750 turned me on to the "asphalt dyno" or plug chop and how to do it correctly. I found that the 125's were too rich and I was gargling gas at WOT. The bike got pulled from service before I could actually test some 115's. Anyway, that is the long story of how I came to giving Hocker my opinion, which as I stated earlier is just a guess at a good starting point. And yes, If his bike is stock there are no clips to adjust needle height.

       

[mrbreeze]

I guess my bike is different but I dunoo.I have heard of of other members runnin the fat jets....CBen for one but he's down under!!!!Still,I have heard of people running the fatties and get better results. My pipe is an Ebay Frankenstein model (I'm sure the header pipe is Kerker and I know the muffler/tailpipe is definetly Kerker with 2.5 inch outlet.) I did run 120's & then 125's but that was before I moved the needle to the #4 click.I like the way it goes now!!!!

[Hockers Choppers]

Just took my carbs off. Geeeezzz what a bunch of crap in the carbs!! The accelerator pump was full! I can't believe it even ran! Anyway I have the pod and the 120 mains and  have the carbs off in my truck and am taking them to work with me tomorrow ( hopefully I'll have time to work on them). I've been riding the bike to work and back, (15 miles both ways, 75-100mph) and it has a little valve train noise and alot of clutch noise. I've set the cam chain and adjusted the valves but the noise seems to be louder at the bottom end. It gets quieter when I pull in the clutch. Is this normal? The bike run fine down the road. Just seems a little noisy?

[jymmeye]

You might try putting the choke on when it starts bogging.  If it picks up it is a lean fuel condition and you have a restriction somewhere.  If it gets worse it most likely is somewhere other than your carbs.

[Hockers Choppers]

Got the bike back together with clean carbs and pods. Had to raise the needles with 3 #4 nylon washers to get the low to mid range right. Haven't synced the carbs yet. I can't tell if the 120 mains are right or not. Haven't pull a plug to see. seems a little rich. Tried pulling the chock at wot and it doesn't pick up, it just dies. Trying 115 next.

[Hockers Choppers]

I guess my bike is different but I dunoo.I have heard of of other members runnin the fat jets....CBen for one but he's down under!!!!Still,I have heard of people running the fatties and get better results. My pipe is an Ebay Frankenstein model (I'm sure the header pipe is Kerker and I know the muffler/tailpipe is definetly Kerker with 2.5 inch outlet.) I did run 120's & then 125's but that was before I moved the needle to the #4 click.I like the way it goes now!!!!

I'm up to 125's and the plugs are bright white still! I've got 130's coming ( local shop had 3 !! ). Is 1978 the only year with the non-adjustable needles? I have to adjust mine with nylon washers.