Topic: Hesitation on Acceleration plus Excessive Backfire on Deacceleration

[Alan F.]

You can pick up the Harbor Freight dial indicator and magnetic base for under $30.

https://www.harborfreight.com/multi-position-magnetic-base-with-fine-adjustment-63663.html?ccdenc=eyJjb2RlIjoiMjAwODQ5MzciLCJza3UiOiI2MzY2MyIsImlzIjoiMTAuMzkyIn0%3D&cid=paid_google|||63663&utm_source=google&utm_medium=cpc&utm_campaign=&utm_content=&gclid=CjwKCAjw2ZaGBhBoEiwA8pfP_ubxYSo2Ke5Gh3aG5xKwpHAR0E13ydYmK0cXs4hHBlTsneXeyDJPGhoC6dUQAvD_BwE

https://www.harborfreight.com/1-in-travel-machinists-dial-indicator-63521.html?ccdenc=eyJjb2RlIjoiMjAwODQ5MzciLCJza3UiOiI2MzUyMSIsImlzIjoiMTMuNTkxOTk5OTk5OTk5OTk5In0%3D&cid=paid_google|||63521&utm_source=google&utm_medium=cpc&utm_campaign=&utm_content=&gclid=CjwKCAjw2ZaGBhBoEiwA8pfP_sL_-bv4QU3tcMwmGc6Dkm9JCX9HWutfCBiwm18Wpl7HbPsLHT035hoCdukQAvD_BwE

I'm sure this won't be the only thing you'll use it for, it may be better than borrowing, your decision matters solely.

Not advancing until 4000? Seems tight. Count the number of windings on your springs and compare with other members springs (Pewe) also get a Vernier  caliper (again HF not digital, ~$20 and good for lots of things like ID o) so you can measure the diameter of your spring wire, maybe the PO swapped out springs? 

I'm curious if your PO as a member here, Chicago CB750F0 may net a member that hasn't been on in a?while, or one that is current and may have good info.

[PeWe]

- If the springs are soft which will make you to retard the plate so F can line up at idle at 1000 rpm, full advance will then suffer.

You can see when springs are sloppy. Advancer in your hand and you can rotate the cam several dergees without any spring force.
It will work better when springs hold it back from the very beginning.
The arms will not move without spring force from start.

- Point gap correct? More will retard more.

Cut the springs and you can set plate correct for idle, full advance,  between the marks at 2600-2700 rpm.
I adjust mine for idle 1100-1200rpm.

My AD125-01 advancer @ 2600 rpm (checked yesterday, Idle - 8000rpm)
K6 stock tacho. Full advance between the '  ' marks.

My earlier setup with TEC 300, full adv at 2700 rpm.

Here when I did it for first time. Very important mod to make bike to run.
http://forums.sohc4.net/index.php/topic,131339.msg1464986.html#msg1464986

[Alan F.]

This transparent points cover was common in 80's. I'll bought mine ca: 1983. Smoke color like tinted visirs to helmets.
I have seen on eBay lately, not cheap.
Insane price!!
Mine costed less than stock Honda!
https://www.ebay.ca/itm/154389843495

Maybe someone can offer new for less.

One of our members makes some really cool stuff for all of the Fours, check out his clear points cover kit:

https://www.fb-stuff.com/

[YoungBlood]

Alan, those custom side covers are saweet! I will definitely keep them in mind when the time is right. Great idea to try to hunt down the PO, perhaps he's on here. I will say this though, the PO I got the bike from only had it for a few months. I believe he scored it for a cheap price and that it was sitting somewhere for a few years unridden (covered). He did a few adjustments and flipped the bike. I wouldn't be surprised if the guy I got it from is on here. But I'd be surprised if the person he got it from is.
I also think it was the PO I bought the bike from who swapped the exhausts. My only clue to this is the fact he gave me a dirt bike helmet when he noticed I don't own one, and that exhaust looks like a dirt bike exhaust.
PeWe, I am uncertain that cutting the springs is the way to go. I do not reach full advance until I am over 3,500, I believe it was about 4k. I am going to check the spring windings, and also see if there is any lack of movement that you were describing.
TT, I still have not tried out the choke, but I am going to very soon. At the moment they are 1/8 turn in, but no noticeable difference. I am going to do another 1/8 turn in today.
I finally received the 1/4 contact point (TEC), so I will install it before work.

There also seems to be a symptom that I barely notice, only when I try to push the bike as hard as it will go. When running in 1st through 3rd gear if I give the bike a lot of increase in throttle it starts to make a sputtering noise out the tail pipe. This does not happen "out of the gate", but after I am pretty far up in rpm. I'm not sure where in rpms I am at since I still don't have the tach-cable. Is this normal? Simply the bike is saying - "hey, dummy, I can't keep pushing like that unless you shift those gears!". On the flip side, bike runs very well again, seems to top out around 105mph. It also has alot of power throughout 5th gear.
My apologies on being away from the thread, I've had work and other things.

[PeWe]

About springs.
Set the ignition so it will line up with full advance at 2500-2600 rpm. In the middle between '  '.

This is how many do, Dyna recommend when setting up Dyna-S.
Idle and engine behavior before that might  not be optimum then.

I think you will not get F ' to line up at idle now. It is too advanced.
When springs are too sloppy, ignition plate need to be retarded very much when advance kick in earlier, maybe max to get idle right.
Plate is rotated max clockwards.

[YoungBlood]

PeWe, the F mark is lined up at idle, approx. 1100 rpm. But when I check the full advance marks, the rpm is well above 2600, approx. 3500-4000. The springs must be too tight, right? Not too loose, if they were loose then wouldn’t full advance occur sooner in rpms than later?
I’ll double check where the plate is set, I think you are correct that I am fully CW in setting for F at idle.
I also will send a video when I have the tach cable installed. This means I won’t be able to give accurate feedback until the weekend. I don’t trust the digital device someone let me borrow. Cheap tach hour meter from Amazon. It may be incorrect by a lot with stating full advance is at 3500/4000.
A completely different matter: I’m noticing a pretty heavy oil leak out of the oil pressure switch. Anyone had an issue like this, and a reputable solution? Say a replacement part that works, whether OEM or not?
Alan, I’ll pick up a dial gauge from HF soon, thanks.

[TwoTired]

I seem to remember you changed the throttle valve needle position.  Before your recent issues, did it run better at the old needle position?

At any rate the spark plug deposits are your window into the combustion process.  So read them. And if you can do a "plug chop" when the engine is misbehaving, those deposits, if different than normal op, can give you clues as to what to seek for remedy.

Have you read the plugs since the ignition change?  Have they ever cleaned themselves after being sooty?   If the center electrode insulator becomes coated with black conductive carbon, you are back to ignition issues, that aren't caused by ignition components, but rather fuel delivery components.

One alternative is to seek out a dyno.  They have exhaust sniffing equipment that will tell you mixture ratios at whatever RPM and power setting chosen, to enable direct change in the areas needed.  You can do similar without dyno expense.  But, it takes more time and a test track to operate at all RPMs and power setting. Your choice.

Cheers,

[Alan F.]

I wonder if the wobble in the advancer stud is contributing to the slow advance and top end 'gurgle'?

Whatever you do, don't tighten your oil pressure sensor. It's easy to cause cracks in the cases this way.

Is it possible that you've over-filled the oil level?

[PeWe]

Point gap OK, not too wide?
0.3-0.4mm (0.0118- 0.01574")

Ignition timing lamp is more stable when using a separate battery.
I use my old bike battery standing close on the floor. No mess with cables and seat open.

EDIT:
The advancer must be lubricated. Grease inside cam and the arm joints.
One thing if springs are totally wrong, different springs.

I have cut springs on 3 advancers and they all act well. F ' at 1000-1200 rpm, full advance 2600-2700 rpm.

Here my last cut after cutting one of the 2. 
AD125-01 advancer, the other 2  TEC 300.
The cut part beside, bent up the spring  to shape a new loop and attached it around the tower.
.

[Kevnz]

I set points using a multimeter on Ohms scale. Connect 1 lead to the blue or yellow wire depending on whether you are setting 1,4 or 2,3 , the other lead to earth. Should read continuity.  Adjust points plate so that meter just reads open circuit at F mark. You can move points plate back and forth and watch when the points are opening and closing. Do 1,4 first then switch to 2,3. Easy.

[YoungBlood]

I seem to remember you changed the throttle valve needle position.  Before your recent issues, did it run better at the old needle position?
TT, that's correct: I changed the needle to the second slot from the top, 4th from the bottom. It's hard to say, I was battling bad condensers, as well as a starved fourth cylinder with a float set too high. Also, I never ran the bike as hard as I have been lately. My rider legs have really stretched out lately, and my confidence handling my bike has as well. I am uncertain I ever was trying to push the bike so hard in 3rd gear before shifting into fourth. I'm unsure whether at the 3/4 throttle range I had a sputtering noise coming from the tail pipe. However, the bike does not hesitate when I am that far deep into the throttle, it's only the exhaust's pitch/noise shifts. 
At any rate the spark plug deposits are your window into the combustion process.  So read them. And if you can do a "plug chop" when the engine is misbehaving, those deposits, if different than normal op, can give you clues as to what to seek for remedy.
I'll be sure to check the plugs, thanks.

Have you read the plugs since the ignition change?  Have they ever cleaned themselves after being sooty?   If the center electrode insulator becomes coated with black conductive carbon, you are back to ignition issues, that aren't caused by ignition components, but rather fuel delivery components.
I have not, but I've been pulling the #4 plug when installing the new contacts and checking timing. #4 seems to be cleaning itself, primarily white around the porcelain with a touch of black.
One alternative is to seek out a dyno.  They have exhaust sniffing equipment that will tell you mixture ratios at whatever RPM and power setting chosen, to enable direct change in the areas needed.  You can do similar without dyno expense.  But, it takes more time and a test track to operate at all RPMs and power setting. Your choice.
This is what I've been needing! Thank you for the recommendation, I was wondering if something like that existed. I googled dyno and a few shops came up around the Chicagoland region. Most are performance racing shops, online someone commented a dyno check costs about $50. I'll definitely look into this... yet I've never been to a track, and that could be fun.
Cheers,

[YoungBlood]

I wonder if the wobble in the advancer stud is contributing to the slow advance and top end 'gurgle'?
I'll look into this, either I'm going to HF this weekend or trying to borrow that dial gauge from a friend.
Whatever you do, don't tighten your oil pressure sensor. It's easy to cause cracks in the cases this way.
A while back, about two months ago when I first getting to know the bike I noticed a few threads were exposed on the sensor. I assumed that it must have been loose, and I used a wrench trying to tighten it. But I remember not being able to tighten it more than 1/16 - 1/8 of a turn. I'm leaving it be for the moment, but I will search for a crack. I don't think it's a crack in the block, but rather its seeping out of the sensor itself...
Is it possible that you've over-filled the oil level?
When I ran very low on oil a few weeks back, I did over fill it by about 2mm on the dipstick. It's already losing oil fast, and that reminds me that I need to get those gaskets: one for the stator cover and oil pan. This winter I'm going to lug the motor into my apartment and do a rebuild with new gaskets.
Thanks Alan.

[YoungBlood]

Point gap OK, not too wide?
0.3-0.4mm (0.0118- 0.01574")

Ignition timing lamp is more stable when using a separate battery.
I use my old bike battery standing close on the floor. No mess with cables and seat open.
Thanks PeWe, when I get another battery next summer I'll use the old one for timing.

EDIT:
The advancer must be lubricated. Grease inside cam and the arm joints.
One thing if springs are totally wrong, different springs.

I have cut springs on 3 advancers and they all act well. F ' at 1000-1200 rpm, full advance 2600-2700 rpm.
How should I tell if the springs are worn? If when rotating the advancer on the crank I see no movement?
This weekend I'll be sure to take the advancer apart to clean and grease everything thoroughly.
Here my last cut after cutting one of the 2. 
AD125-01 advancer, the other 2  TEC 300.
The cut part beside, bent up the spring  to shape a new loop and attached it around the tower.
.

PeWe, I believe my springs must be too tight at the moment because it advances so late. However, I'll get back to you this weekend after a correct timing read, lubricating the inside came, and checking the run out on the bolt holding the advancer.

[PeWe]

I doubt springs can be too tight if they are stock, not cut ones.  If replaced by other springs another thing.
See my photo where 1 spring is cut, the one to the left.

Replace the advancer if you do not trust it. TEC 300 or AD125-01.

BUT, you started  this thread with this: Something changed or is it F at idle?

"Point gapping 1/4 is at .012
Point gapping 2/3 is at .016
Timing on 1/4 is dead on with F mark
Timing on 2/3 is just a tad retarded because I cannot adjust my plate any more"

[YoungBlood]

The plate is no longer fully CW, both 1/4 and 2/3 are on the F mark when I did dynamic timing at idle. 1/4 is at .014, 2/3 is at .013.
I’ll check the springs out when I fully disassemble the advancer this weekend with what you’ve said in mind. But I want to double check with the tach cable where the rpms are. This might be a red herring case.

[PeWe]

That plate is advanced.

[TwoTired]

I don't think it matters where the plate sits, as long as the timing and dwell (gap) is correct.

However, new points are to be set at .016 in. So that the dwell is factory.  Used points with irregular contact surfaces are set to .012, as the pitting makes the setting wider (actual).  Or with a dwell meter.   

Only use metal devices to get the points flat again (file).  Nearly all other abrasives are sacrificial, leaving bits of non-conductive grit in the point surface, reducing contact area and speeding the burning, pitting process.  Use the latter only in dire emergency.

My thoughts.

Cheers,