Topic: 2nd opinion on carbs needed

[zerodaydave]

Yeah - I did. I measured the floats and did a clear tube test. I screwed some clear tube in the drain hole and let the float bowls fill up. They seemed good to me. I can do it again and post a pic. I can't run a 1/4 1/2 and full idle chop now because the bike breaks down after riding for 30s - 1m also now power. I'm going to do the idle chop now.


Sent from my iPhone using Tapatalk

[Jimray23]

Ok let us know how it turns out

--------------------------------------------------
Jim
I really don't see why people ask for advice if their not going to take the advice given.

[evinrude7]

i hate to say this dave but all the trouble you are having could most likely be solved by putting the stock airbox back on. 

[zerodaydave]

i hate to say this dave but all the trouble you are having could most likely be solved by putting the stock airbox back on.

Haha I'm looking at options for an air box now amigo. I understand. Thanks.



Sent from my iPhone using Tapatalk

[evinrude7]

i hate to say this dave but all the trouble you are having could most likely be solved by putting the stock airbox back on.

Haha I'm looking at options for an air box now amigo. I understand. Thanks.



Sent from my iPhone using Tapatalk

when i got my bike the PO had pods on it.  ran like garbage.  found a stock airbox on ebay.  changed everything. 

[flybox1]

Just do the idle chop and get back to us....

[scottly]

My main jet was 102 on the trip increased to 105 stock now which is when the problem started. Pilot is 40 (replaced old pilots with new 40s.) Both are Kehnin stamped.

Try going back to the original 102 jets and report back.

[zerodaydave]

Hey everyone -

Happy 4th.

I finished the idle chop. Here are the results 1 plug from the 1/4 coil and 1 plug from 2/3 coil. I let the bike idle for 7m. I put a fan on it but I did have to choke it a lot to get it started at first because I didn't know I was actually out of gas so I ran wot for about 1m until I switched it to reserve and then let it idle.

I also went back and tried the 102s that were working fine and I was having the same issue.

I went out and bought new jets from jets r us and now I'm running 40 slow and 108 main.

I'll take it for a test drive and report back the results.


Sent from my iPhone using Tapatalk

[zerodaydave]

Update: I just went on a small ride to get gas and groceries. The bike made it! So progress I can make it around the block now.

Like I said earlier it's running 108s and 40s from JetsRUs. Air screws are at 1 1/4. The main is great an no longer cuts out. Mid as well seems good. Pilot is still having issues. From idle to acceleration the bike continues to be an issue. It bogs down for - second or two then catches. Additionally the bike is backfiring through the exhaust when I let off the throttle.

Does anyone have a good tutorial on timing for a CB750?


Sent from my iPhone using Tapatalk

[PeWe]

Ignition timing http://www.hondachopper.com/garage/carb_info/timing/Static_and_Strobe_Timing.pdf

I recommend doing the point gap with a dwell meter. Done and discussed here:
http://forums.sohc4.net/index.php/topic,147444.0.html

[zerodaydave]

Here are the plugs after a 75 mile canyon run. Bike made it! Mid feels flat. On the uphill it loses power. I'm running 108s / 40s at 3/4 turn out on the air screws now. Needles in the 2nd position from the top still. Slight backfire in exhaust when letting go of the throttle. Carb spitting very intermittently (like twice during the entire 75 mile ride).

[flybox1]

Here are the plugs after a 75 mile canyon run. Bike made it! Mid feels flat. On the uphill it loses power. Change gears I'm running 108s / 40s at 3/4 turn out on the air screws now. Needles in the 2nd position from the top still. Slight backfire in exhaust when letting go of the throttle. indication of lean  Carb spitting very intermittently (like twice during the entire 75 mile ride).

Plugs look lean. Exh popping = lean....id say you are lean. 
@ what throttle position did you experience the flatness/backfire. etc?  (rpm doesnt tell us what fuel circuit is being used at that moment)
If around 1/3-1/2 throttle...drop your needle clips to 3rd from the top..
If anywhere over 1/2 throttle, go to 110 mains.

[zerodaydave]

Here are the plugs after a 75 mile canyon run. Bike made it! Mid feels flat. On the uphill it loses power. Change gears I'm running 108s / 40s at 3/4 turn out on the air screws now. Needles in the 2nd position from the top still. Slight backfire in exhaust when letting go of the throttle. indication of lean  Carb spitting very intermittently (like twice during the entire 75 mile ride).

Plugs look lean. Exh popping = lean....id say you are lean. 
@ what throttle position did you experience the flatness/backfire. etc?  (rpm doesnt tell us what fuel circuit is being used at that moment)
If around 1/3-1/2 throttle...drop your needle clips to 3rd from the top..
If anywhere over 1/2 throttle, go to 110 mains.

It was 1/4 - 1/2 flat. And 1/2 - full flat. I will try the needs first to the 3rd position. And then I will try the 110s.

Adjusting the idle mixture screw eliminates the popping somewhat but it's still there. Air screws are at 3/4 turns out.

[zerodaydave]

I'm making some progress. I dropped the slide needles to 3rd position. Bike is no longer flat at  1/4 -3/4 throttle but as soon as it hits 3/4 throttle the bike cuts out. As I continue to rev through wot it recovers but it's flat. No popping, or spitting. I also did another plug chop. I let the bike idle for 5 minutes with new plugs. Air screws are at just 1/2 turn and the plugs are very lean! No color at all. I'm already at 1/2 turn from lightly seated. Should I continue turning in or go up a size (I'd rather not do that).

I'm running 108 main , 40 slow , slide needles in 3rd position, air screws 1/2 turn.


Sent from my iPhone using Tapatalk

[evinrude7]

you're probably at the the tipping point.  get the larger jets and set what happens.  i haven't read all the replies but i guess you're trying to jet for pods. 

[flybox1]

I'm making some progress. I dropped the slide needles to 3rd position. Bike is no longer flat at  1/4 -3/4 throttle but as soon as it hits 3/4 throttle the bike cuts out. As I continue to rev through wot it recovers but it's flat. No popping, or spitting. I also did another plug chop. I let the bike idle for 5 minutes with new plugs. Air screws are at just 1/2 turn and the plugs are very lean! No color at all. I'm already at 1/2 turn from lightly seated. Should I continue turning in or go up a size (I'd rather not do that).

I'm running 108 main , 40 slow , slide needles in 3rd position, air screws 1/2 turn.


Sent from my iPhone using Tapatalk

40s are stock for your carbs, so going to 42s is not unrealistic for pods.  Yeah, it bites that they are $11ea @ jetsrus....but on the bright side, get a set of 112 or 115 mains at the same time.  Sounds like you need them.  With dialed A/F mix, your bike should feel like it wants to continue to pull past redline...
Once going up to 42's, idle plug chop first to get your air screw set.  Then go on a run.

[zerodaydave]

Thanks man.

I'll try the 42's and increase my main to 110 and post back. Idle chop first.

Also I've been looking at this instead of pods.

https://cognitomoto.com/products/cb750-air-intake-box-sohc-and-dohc

[flybox1]

You're so close to tuning this and you want to go another intake?  rofl smh 

Go to 112s or 115s... 110's might still not be enough

[zerodaydave]

Copy on the 112's. I'll skip 110. Putting the order in now.

I'm just getting frustrated with it. I know I'm close. The mid range feels a lot better now. No popping or spitting so that's good. Still not feeling comfortable with the SLOWS or MAIN. SLOWS at only 1/2 turn out and still lean just does not feel right.

[flybox1]

Yeah...I know. 
With the 42's, you'll be able to go closer to 1 turn on the air screws.  More in the middle of their tuneable range.
112 mains should be really close, with your needle clip where it is.

[zerodaydave]

My poor bike ... haha. I've been running lean for so long. I put the new 112, 42 jets in tonight. Needle is in the 3rd position. Off idle is amazing. No hesitation. Lots of power. As soon as I roll into 1/4 throttle the bike cuts out and it continues to cut out to WOT. If I roll off the throttle the bike  recovers at 1/4 throttle. I've posted a video here. I'm wondering if I should go up to 115s? I should get the main jet right first before screwing with the needle position is that correct? What makes me think I might still be lean is the plugs are still whitish (although they are getting darker) and it did spit once through the carbs on a 30m ride. Carbs are synced. No plug chop yet. I do have a set of plugs but I'm waiting until I get he jetting somewhat right. Also if I switch the mains do I need to resync the carbs again? Does changing the mains mess with the vacuum?


Sent from my iPhone using Tapatalk

[Jimray23]

It sounds like you need bigger needle jets

--------------------------------------------------
Jim
I really don't see why people ask for advice if their not going to take the advice given.

[zerodaydave]

Forgot to post the video. Also I should add since I had the carbs apart I cleaned all the passages, checked float buoyancy, cleaned the needle valves, and checked the float bowl overflow stems for cracks.

https://sohc4-forum-attachments.s3.amazonaws.com/trim.D9839835-6B2C-4F73-8036-3A4D12F575C6.MOV

[zerodaydave]

Well I think I'm at the tipping point. I'm at 115s, 42s, and needles in the 3rd position. Air screws 1 turn out. I took it for a ride today and I can cleanly rev through the entire throttle range. Only slight popping when  closing the throttle - not to bad at all. The mid range feels slightly off to me in terms of power (feeling flat) but I think I'm going to give it a few days before I decide to move the needles to the 4th position from the top. The bike has really opened up and I'm psyched to report my plugs are tan now! Thanks everyone for your help! In the past I would have brought this bike to the shop and I would have gotten it back running worse than when I brought it in. I'm psyched on everything Ive learned from you all. Cheers.


Sent from my iPhone using Tapatalk

[flybox1]

Yeah...those are looking nice.    Glad its getting better.