Topic: Dragging clutch? Can't go over 10 MPH

[Xxthegonzxx]

That model uses an accelerator pump make sure the diaphram is not cracked.  You can check quick throttle twist with the airbox off.  If your accelerator pump is working it will squirt gas into all 4 carbs.  If you can gradually gain speed by slowing applying more throttle that that would be my guess.

What speed were you able to get to.

Thanks Chewy! The Accelerator pump is working fine I took the box off and saw it squirt gas in all 4 carbs.   I'm pretty sure it's a jetting issue. I'll come back with an update on what happened probably sometime next week.


Sent from my iPhone using Tapatalk

[LesterPiglet]

Even with the headers removed from my bike I can still go pretty darn quick. Don't worry about your exhaust causing problems at the minute.

[grcamna2]

When you do the jetting it might be good to use the Original air box with a high flow filter for the best low-midrange performance.

I have the original air box with a k&n filter

That should work.

Sent from my iPhone using Tapatalk

[Black 750K8]

Even with the headers removed from my bike I can still go pretty darn quick. Don't worry about your exhaust causing problems at the minute.

I agree it is more than just  exhaust .

[TwoTired]

That model uses an accelerator pump make sure the diaphram is not cracked.  You can check quick throttle twist with the airbox off.  If your accelerator pump is working it will squirt gas into all 4 carbs.  If you can gradually gain speed by slowing applying more throttle that that would be my guess.

What speed were you able to get to.

Thanks Chewy! The Accelerator pump is working fine I took the box off and saw it squirt gas in all 4 carbs.   I'm pretty sure it's a jetting issue. I'll come back with an update on what happened probably sometime next week.

The accelerator pump supercedes jetting for throttle twist response.  It not only has to pump but it has to pump a very strong stream and evenly for each carb.  When it works properly, the engine will zoom no matter how hard or fast you twist the throttle.  The fuel jets then maintain the required fuel flow after the RPM is attained.

The pipe links between carbs have a restrictors inside them to keep the pump volume even at each station.  The restrictors often get thrown away by some rebuilders, which means that all carbs don't pull their proper weight.

Both the check valves must open and alternately seal properly, and the diaphragm's mickey mouse ears ears must not be swollen closed which limits flow volume.

[bsalem77]

Check your coils I replaced mine cause I wasn't getting any power.  Was only running on 2 cyl.     


Sent from my iPhone using Tapatalk

[Xxthegonzxx]

This sucks, I had a long post that I was typing and the page I was typing it in crapped out so this is going to be a shorter version.

Took it into the shop and they basically charged me an arm and a leg for a "restore". Told them that I would only want them to take a look at the jetting instead of the full list of items they recommended and they declined. What a waste of my time!

Anyway, the lesson here is that if you are working on your bike and your bike is your baby then you should treat it as such. No one else is going to know it as much as you.

What I'm going to do from here is try to fix it myself. So let's revisit what's happening...

The bike idles fine. As soon as it's warmed up i take it out for a ride, drop it into first and disengage the clutch slowly. While riding the friction zone on first and twisting the throttle about 1/3rd of the way the bike sounds like it's struggling. RPMS are around 3k and it starts to take off very slowly. I get to around 15 MPH and it still sounds like struggling to get speed. I shift into 2nd gear, disengage the clutch and now it does the same with 2nd although now it feels like it's gaining some speed. If I twist the throttle more and more the RPMS shoot up and the bike slowly start going faster. It definitely sounds a little healthier and it starts picking up speed. Since it's a brand new engine and new rebuild I don't push it any more. I take it around the block a few times and it's the same. Whenever I come to a stop sign it dies sometimes as well. I have to keep revving the engine for it to stay running.

So those are the issues I've been experiencing. What I'm going to do from here is switch out the Open Kerker exhaust and install my old stock cb750F SS 4-2-1 exhaust. I'll take it around the block and see how it runs. If it runs better, like it did before I installed the new exhaust, then that means it's probably a jetting issue. If that's the case then the next steps would be to buy a bunch of different size carb jets that are higher than my stock (105 Main and 35 Slow/Pilot). Does that sound about right? Am I heading in the right direction? I'll update everyone with what happens.

[74750k4]

If you change things back towards stock, ONE at a time, you might learn which one/s are causing your issue. Sounds like fuel for sure, and not enough of it...

[Don R]

Have you checked float levels? One size of jet won't cause this.

[Airborne 82nd]

First off I am new to these bikes. Now I see you can get it up to 3K rpms but no speed you say it is a newly built engine I'm wondering just how tight this thing is when you get it up to full temp pull the plugs and see how hard or easy it turns over with the kicker by hand just to rule out that something is to tight it should turn easy. would not take long and then you could check that off.

[TwoTired]

My money is still on the accelerator pump circuits.

[Xxthegonzxx]

So I finally fixed the issue. It turns out it was the clutch.

I ended up putting the stock exhaust back on and took the bike for a ride. Things were still the same so I continued on what I recently did to the engine. I changed the clutch recently and opened it up to double check it again. That's where I found that the clutch wasn't installed sufficiently (my dummy mistake). It wasn't properly seated inside the clutch basket and the friction disk with the thickest tab was sticking out a bit. I reassembled the clutch, double checked the clutch cable and tightened things up. After that it ran like a dream! Thank you all for the great tips and remember to have patience! I can't tell you how many times I pulled my hair out because of this.


Sent from my iPhone using Tapatalk

[Airborne 82nd]

I don't understand that at all I would have thought it would slip and the engine would race but no speed. Maybe if Mr. TT comes back he or someone could explain this to me. I usually thing of the clutch as a go or no go type thing it engages but not enough and slips or  doesn't disengage. and it is hard to shift like a broken cable.

[Xxthegonzxx]

I don't understand that at all I would have thought it would slip and the engine would race but no speed. Maybe if Mr. TT comes back he or someone could explain this to me. I usually thing of the clutch as a go or no go type thing it engages but not enough and slips or  doesn't disengage. and it is hard to shift like a broken cable.

One thing that led me to check the clutch was that I was able to roll it very easily while in gear. Never noticed it because it was just sitting and Idling most of the time but once I tried that I knew that something was wrong. It was almost as if it were in neutral on all gears. So weird.


Sent from my iPhone using Tapatalk

[Don R]

?

[74750k4]

I don't understand that at all I would have thought it would slip and the engine would race but no speed. Maybe if Mr. TT comes back he or someone could explain this to me. I usually thing of the clutch as a go or no go type thing it engages but not enough and slips or  doesn't disengage. and it is hard to shift like a broken cable.

One thing that led me to check the clutch was that I was able to roll it very easily while in gear. Never noticed it because it was just sitting and Idling most of the time but once I tried that I knew that something was wrong. It was almost as if it were in neutral on all gears. So weird.

Sent from my iPhone using Tapatalk

The original Post Title was "dragging" clutch. But now, you say "I was able to roll it very easily while in gear" THAT is a SLIPPING clutch, and as such, would also enable you to rev the crap out of it in any gear. Never heard that mentioned...  even now.

[TwoTired]

In the computer industry there was a saying regarding the ability to solve problems:

Garbage in equals garbage out.