Topic: #4 Not getting hot - Swapped 4 and 1 wires and #4 still not working.

[briancwynn]

Okay all sorry for the question as this is my first bike so of course I could have another issue.  The issue, I am unable to put my POD covers on the Carbs and run the bike. If I add them, the bike will bog down when attempting to accelerate. The bike will idle fine.   Without the pods the bike runs pretty good to around 40mph where the bike does not want to accelerate much faster after.  I can get to around 60 but the bike does not want get there very fast.

The Carbs have been professionally restored and cleaned.  The settings are 125 main jets, stock slow, and 2 shims on the needle

I have been told my Jet size is too small and believe this is the reason for the slow acceleration after 40. 

If they do need to be bigger, do i only replace the main jet and what brand and size is recommended.  Do I need to change anything else with the carbs?

Thank you.

[flybox1]

it depends on where your 'bog' is....you need to 'fix' the air/fuel mixture at that throttle position.
speed is really irrelevant for mixture tuning.  be more concerned with throttle position, and what jet, or combinations of jets are supplying the needed fuel in that moment.
answer this...at your '40mph' when you feel the bogging, what throttle position are you at?  Are you in 5th gear and just barely turning the throttle, or in 1st gear and at WOT? 

for starters, your stock #35 slow jet is too small.  to show yourself this, install your pods, install a NEW set of NGK D8EA plugs, and let your bike idle under a fan, for 3-4 minutes.   pull the plugs and post up a picture here of the insulator color.  They should be just showing light tan, but i would bet they are pretty white.
If they are, i'd suggest starting with 40 pilots, and 1.5 turns out on the mixture screw, and retest.

BTW, how thick are your shims, and do they sit down in the pocket of the slide? 
(2 shims @ 1mm each sets a different needle height than 2 shims at .5mm ea  )

what 4:2 exhaust do you have and does it have baffles or is it open?

[Duke McDukiedook]

As most will recommend I think you should put the breadbox back on and make sure the bike runs well with that setup.
Then you can fiddle with ze podz to your heart's content after you KNOW the bike is running correctly.

[700504]

I run pods, and a 4-1 with almost no baffle. 38 pilots, 2 shims (.22 mm each) and 120 mains. Pilot screws are about 2 turns out. Runs great, cruises on the free way just fine. As a side note I'm also at elevation of around 185'. Did many plug chops over the last 2 years to dial it in and now they come out looking nice and brown.

[briancwynn]

Okay all,
I started in to do this Plug chop and I found out that exhaust on 4 was not getting hot to touch. All others are smoking to touch but #4 was cool.  I am thinking I am not getting spark or no combustion in #4.  What to check next on this is my questions.  I pulled the spark plugs in 1 which is working and 4 which was not working and they both look similar.  Seems like 4 just stopped firing recently?   The coils are the OEM on this from the 1978 bike.   
Please see pictures below.  Any suggestions as I just took her for her first real trip and she did great. 

[Jerry Rxman Griffin aka MuthaF'er]

Swap plug wires 1 & 4 and see if the bad firing follows the plug wires. If so then you can swap plug caps and see what happens. 1 & 4 both fire at the same time.

[briancwynn]

Jerry, thank you.  If sitting on the bike 1 is far left and 4 is far right correct.  Just to make sure I am not assuming anything.

[700504]

If down the road you still cant figure it out; take your carbs off the bike and gas tank off the bike, put the palm of your hand over the carb boot to the cylinder in question, give the bike a few kicks and then see if it makes a vacuum suction with your palm or feels like it blowing against your hand or if there's no change at all. The quick and dirty compression test, I found out I had a bent intake valve this way ie, one cylinder not getting hot.

[flybox1]

you'll need to go to 42 pilots(3/4 to 2 turns out on the fuel screws depending on plug color)
125 mains might be a bit big...how does your bike perform at mid throttle...if its sluggish, and you  havent make needle clip/shim adjustments, go down in main and lower one notch/add a shim, retest. 
Buy OEM Keihin jets ONLY
Ensure your bowl fuel levels are perfect before performing plug chops/ jet testing.  a slight difference will make testing that much more difficult.

[madmtnmotors]

125 mains might be a bit big..

+1

I just increased displacement of my K8 CB750 from 761cc (62mm pistons) to 836cc (65mm pistons). With a MAC 4into1 header and muffler, a K&N filter in the stock airbox, I figured more displacement=bigger jets, right?

Wrong. Mine would fall flat on its face over 5000rpms with 125 mains when the main jet is "all in". Wayyyy too much fuel. Reverted back to the 110 mains and all is well, pulls hard all the way to 8500rpm. Plug chops still required, but the 125's were way too big for mine...

[HondaMan]

125 mains might be a bit big..

+1

I just increased displacement of my K8 CB750 from 761cc (62mm pistons) to 836cc (65mm pistons). With a MAC 4into1 header and muffler, a K&N filter in the stock airbox, I figured more displacement=bigger jets, right?

Wrong. Mine would fall flat on its face over 5000rpms with 125 mains when the main jet is "all in". Wayyyy too much fuel. Reverted back to the 110 mains and all is well, pulls hard all the way to 8500rpm. Plug chops still required, but the 125's were way too big for mine...

Right. Changing displacement does not alter the air-fuel mixture thru the carbs.

[briancwynn]

Okay all, I found a loose black white wire to the coils for the ground I believe.  I think that it got pulled loose putting the tank on after the rewire.  Anywho I have re-terminated this and found that I still do not have any heat from number 4.  I tried to swap the wires from 1 to 4 and they do not reach for me to check for spark.   So I am going to replace the coils and sparkplug caps if you think its wise.  The original one is very old and its an update to the bike as a whole. 

Question 1.  If the loose wire were the cause it would have cause 2 cylinders not to fire correct?
Question 2.  If I am replacing the coils and the spark plug caps is there anything specific on the caps i need to look for?  I found some on Dime City called  VB05F and SB05F spark plug.  This should be fine correct?   

After I install this I will do the chop on the bike as well. 

Thank you.

[briancwynn]

I traced the black white wire to a double connector (with only 1 connection)  grounded to the frame right above the coils with another black white wire connected.  This black white was from the other side of the coil.  I will take a picture and send to you.  Thanks as always Cal!

[briancwynn]

It was not the blk/white for the coils it was seemingly from the After Market instrument panel.  Thanks Cal.

  Now what is the best way to check for spark?   Can I pull the plug out and ground it to the engine and check for spark?  Another way to test for this?

[briancwynn]

Checked the wiring and still no heat on #4.  If it just stopped working I am hoping its the wires.
Checking the sparkplug boot the end is a screw on and I am not sure this is working well.  Any other ideas to check on?

[briancwynn]

Okay all,
I just swapped the sparkplug boots from 1 to 4 and no change in 4.  I have confirmed the wires and coils are working accordingly but I am not getting a spark in #4.   
What is the next thing to check or is this an engine issue at this time?

Thank you.

[Gene]

Maybe I missed it - did you ground the 4 plug to the head and check for spark?  Did you trim the #4 wire back a little (1/4" +/-) to get a better connection on the cap?  Did you replace the plug?  I had a dead #4 once, new plug - all of a sudden, like magic . . .

That, plus what Cal sez.

[briancwynn]

Gene,
I did not do the ground to the engine and view the spark test as not recommended.  I did swap wires from 1 to 4 and the same issue with cold#4
I replaced the sparkplugs for 1 and 4 as well.   Thanks for the help. 

What is next?

[Gene]

Check your points.  Check for spark.  Check the timing. If the plug to the head test was not recommended you can always just hold the wire and turn the engine, see if you jump.  I'm only half kidding.

Also, and I'm not being rude, swear - you have the choke off while running, yes?

[Gene]

One other quik check. See if spark is jumping (arcing) from the plug wire to the head. Or-come to think of it, are the wires going to the correct plug?

[briancwynn]

All, After I ran the bike with a brand new plug in #4 that is running cold I took the plug out and it looked kinda wet? Not sure so I took a picture of it exactly.  It was not dripping with fuel.. So maybe its not getting any gas.  I think all of my plugs looked lean =More Air than Gas in my mind. 
Please see attached.   Thoughts?

[HondaMan]

All, After I ran the bike with a brand new plug in #4 that is running cold I took the plug out and it looked kinda wet? Not sure so I took a picture of it exactly.  It was not dripping with fuel.. So maybe its not getting any gas.  I think all of my plugs looked lean =More Air than Gas in my mind. 
Please see attached.   Thoughts?

All of your posts sound suspiciously like a bad coil wire, up inside the coil. This happens due to age and corrosion. My own 750 suffered this in 2006, on the 2-3 coil, when the #2 stopped firing and the plug would come out wetted - much like yours. The manufacture of these coils is: the spark wires are welded to the coils' (solid) wire and then the whole subassembly is laid in an injection mold, where the coil body is then molded around those wires. In short, they are NOT replaceable, at least not safely.

You can get some new coils from Honda ($150 per set) or you can use the ones from PartsNmore (Sakura brand, $40 each) for the CB750. I have these on a couple of bikes and they work well, but you will have to make some connectors up to attach them to the bike, as theirs are a 1/4" blade where Honda's TEC coils use the little bullet connectors. In any case, MAKE SURE the coils you use are the CORRECT OHMS on the primary side, about 4.5 ohms for your bike. Some vendors out there are selling lookalikes that will bolt into place, but are 2.5 ohms for CDI bikes instead, which will cause serious electrical troubles in yours.

[briancwynn]

Hondaman thank you. 
So you believe its an issue with the Coils even with the switch done on 1 and 4 of the wires and 4 still staying cold?   I am glad as replacing the coils I can do.  I am going to order parts now.
Thank you.

[disco]

So the header pipes on No's 1, 2 & 3 were getting hot right? You swapped plug leads No's 1 & 4 and No 4 remained cold. No 1 was still hot with the No 4 lead fitted right? Only explanation is a dud spark plug in No 4.

[briancwynn]

Disco, New plug in #4 as well. I will try another one.