Hesitation / Poor running

[Griffin]

My 1980 cb750 had been a great project but I just can't get it running quite right.

I had a hanging idle issue and slight hesitation around 4000 rpm so I turned the fuel screws in a tad and that stopped the hanging idle but the slight hesitation issue I had got a lot worst. Turning the screw back gives me the hanging idle problem again. It's like it's either too rich or too lean without being able to find the perfect spot.

I'm thinking it's not really a carb issue now. After reading about some ignition problems here, I wonder if that's what's going on. I'm using a very small battery that is 5 CCA. I want to replace it with a 150CCA lithium. Any chance that fixes my issue? Maybe the small battery is limiting power to the coils causing a weak spark?

Here is what I've done so far.
Had valve lash set at a shop.
Verified valve timing.
Verified ignition timing at idle.
Verified there is no vacuum leak by spraying carb cleaner on the boots and nothing happens.

I am running a Murray's Carbs dual carb kit.

Have not tested full advance yet.

Hoping to figure this out without taking it to a shop. I really want to learn and fix it myself.

[TOOLS1]

Hanging idle is usually caused by a lean condition such as a vacuum leak. Often this can be cured by adjusting the pilot screws to richen the mixture. Another thing could be that the carbs are not in sync.
TOOLS

[Griffin]

Thanks, Guess I'll get new carb boots and a vacuum gauge set to sync the carbs with.

On Nov 6, 2016 11:17 PM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

Hanging idle is usually caused by a lean condition such as a vacuum leak. Often this can be cured by adjusting the pilot screws to richen the mixture. Another thing could be that the carbs are not in sync.
TOOLS

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NAML

[Griffin]

Putting new carb boots on. Clean the intake ports as I go. Half way done here's hoping.

On Nov 7, 2016 8:10 AM, "Dave Arnold" <[hidden email]> wrote:

Thanks, Guess I'll get new carb boots and a vacuum gauge set to sync the carbs with.

On Nov 6, 2016 11:17 PM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

Hanging idle is usually caused by a lean condition such as a vacuum leak. Often this can be cured by adjusting the pilot screws to richen the mixture. Another thing could be that the carbs are not in sync.
TOOLS

---

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[Griffin]

New carb boots are on and lithium battery in. Sounds better already. Going for a ride shortly. I did find several cracks in the old ones. Can't say if they cracked taking them off or if they were already cracked.  The cracks were all at the engine where I couldn't see them. Needless to say they needed replacing.

On Nov 19, 2016 10:29 AM, "Dave Arnold" <[hidden email]> wrote:

Putting new carb boots on. Clean the intake ports as I go. Half way done here's hoping.

On Nov 7, 2016 8:10 AM, "Dave Arnold" <[hidden email]> wrote:

Thanks, Guess I'll get new carb boots and a vacuum gauge set to sync the carbs with.

On Nov 6, 2016 11:17 PM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

Hanging idle is usually caused by a lean condition such as a vacuum leak. Often this can be cured by adjusting the pilot screws to richen the mixture. Another thing could be that the carbs are not in sync.
TOOLS

---

If you reply to this email, your message will be added to the discussion below:

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NAML

[Griffin]

Runs better but still not great. Starting to think it could be the timing advance. Going to test it next. Still the same issues right now. If I turn the fuel screws in it runs bad, turn them out and get hanging idle. I read somewhere hanging idle can be a bad timing advance. If the advance test fine I guess I'll find a vacuum gauge to test carb sync. Still haven't bought one yet.

On Nov 19, 2016 2:19 PM, "Dave Arnold" <[hidden email]> wrote:

New carb boots are on and lithium battery in. Sounds better already. Going for a ride shortly. I did find several cracks in the old ones. Can't say if they cracked taking them off or if they were already cracked.  The cracks were all at the engine where I couldn't see them. Needless to say they needed replacing.

On Nov 19, 2016 10:29 AM, "Dave Arnold" <[hidden email]> wrote:

Putting new carb boots on. Clean the intake ports as I go. Half way done here's hoping.

On Nov 7, 2016 8:10 AM, "Dave Arnold" <[hidden email]> wrote:

Thanks, Guess I'll get new carb boots and a vacuum gauge set to sync the carbs with.

On Nov 6, 2016 11:17 PM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

Hanging idle is usually caused by a lean condition such as a vacuum leak. Often this can be cured by adjusting the pilot screws to richen the mixture. Another thing could be that the carbs are not in sync.
TOOLS

---

If you reply to this email, your message will be added to the discussion below:

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NAML

[Griffin]

Problem still exists after replacing the carb boots.  Still need to test the advance.  I'm also thinking about replacing the coils, wires, and plug caps.  Even if new coils don't fix it I'd like to have new ones anyway, but fixing the problem would be a huge bonus.

I'm also going to get a carb sync gauge to make sure my carbs are synced.

I found an Accel Super Coil Kit that is cheaper than buying OEM parts but more than buying cheap stuff. Anyone use them before?

I also ran compression tests and a leak down test.  My compression is low at 90psi per cylinder and the leak down shows 40% loss.  I hear the air through the crank case so I believe that means my head and valves are good but most likely the rings are bad. Now having that said could my low compression cause the hesitation issues? Or I'm I just loosing some horse power?

My question is can I get this thing running better without installing new rings?  Lastly it seems it should be done so how difficult is it.  I've pulled the engine and did the head work myself.  Seems like pulling the cylinders off and installing rings would not be any more difficult than that but I don't know what I don't know.

[Griffin]

Maybe someone could also recommend a set of vacuum gauges that will work with the DOHC ports.

[TOOLS1]

This set will handle any carb setups out there.
http://www.ebay.com/itm/Universal-4-Motorcycle-Gauge-Four-Carb-Carburetor-Carburetter-Synchronizer-Set-/381725346356?hash=item58e09a8a34:g:SMYAAOSwzaJX-o9e&item=381725346356&vxp=mtr
TOOLS

[Griffin]

Spent some time trying to sync the carbs tonight. It's a bit different with 2 carbs for 4 cylinders. I got them pretty close but I can't seem to improve beyond 2 marks difference between the left and right. Idle is 9 and 11 they go up and down together. I may try to adjust the left a little more to see if it will improve but the last adjustment didn't seem to do anymore to improve it.

At this point I'm certain I need new rings. The number 2 plug fools a lot and that header always seems cooler. I think oil is getting past the rings making it act like it's rich at least in number 2. Pretty sure that's why I can't get the left and right to balance either.

Thoughts from the group? Anyone agree or disagree?

There is always a complete ring kit on eBay for 58.00 anyone use that before? That's half the price of OEM. I think I'll replace the bottom gasket and the 4 O-rings while I'm at it.

[Griffin]

I decided to fix the root cause of the running issues, bad rings. I purchased the Wiseco 823 kit and have the cylinders at a machine shop. Also order an oem cam chain B. Looking forward to having it all back together again in time for all the great riding weather.

 

[Griffin]

Quick question. Just got my bored cylinders back. I noticed orange rings around the jugs were they come out on the bottom. The machine shop guy said I should use new O-rings. They he salvaged 2 but couldn't save two. If I order new o-rings do I scrape off the orange stuff? I'm not sure if that is the old O-rings or if it's something else. I saw a kit of black O-rings on eBay cheap enough. I can post a pic of the cylinders if needed.  Looking forward to getting it back together.

[TOOLS1]

I have seen orange, black, and even green O-rings on the bottoms of the cylinders. You need to dig them out and replace them. They come with the gasket sets.
TOOLS

[Griffin]

Thanks for clearing that up for me.

On Apr 29, 2017 5:42 PM, "TOOLS1 [via Vintage and Classic Honda's]" <[hidden email]> wrote:

I have seen orange, black, and even green O-rings on the bottoms of the cylinders. You need to dig them out and replace them. They come with the gasket sets.
TOOLS

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NAML