Topic: Spark Advancer Question.

[SOHCiro]

Hello,

I didn't like how jerky my bike was, the sudden pull at 1500rpm. The throttle would also hang unless rolled back manually.
Thinking the springs were sloppy, I tried Hondaman's method of cutting coils off springs.
I then set gap and static timing.

With a timing light, it shows idle (1000rpm) is too advanced (F mark on the left of the index mark), and retarded at 2500rpm (2 lines on the right side of the index mark.)
The spark only reaches full advance at approx. 4000rpm.

If I retard the idle for better idling, it would reach full advance later, say around 4500. Thats almost unpleasant to ride...
If I advance too much to achieve full advance at 2500rpm, it would cause hard starting, also unpleasant.
Also, I don't understand why it would show too advanced at 1000rpm, because cutting the spring should slow the rate of advance.

Am I correct in these theories?

Thanks!

[scottly]

The spark only reaches full advance at approx. 4000rpm.

This means the springs are now too tight; full advance should happen about 2500 RPM.

[SOHCiro]

-Scottly,
Yes I understand that, however I'm wondering if it were too tight, why would it be too advanced at 1000rpm?

[scottly]

If timing is advanced at 1000 RPM, it's not set properly. Adjust the timing so the F mark is aligned at 1000 RPM when checked with the strobe. This is best done on a trial-and-error basis; observe the timing, shut the bike off, rotate the point plate in the desired direction, tighten the plate screws, and check with the strobe. Repeat as required.

[dave500]

forget the f mark,with the strobe increase rpm watching the timing advance,once it stops advancing set it between those two full advance marks,dont worry where it is at idle,once riding the bike itll be at full advance most of the time anyway.

[SOHCiro]

Thanks.
I've drawn an illustration of spark timing.
From my understanding, the ideal timing is (B), where the spring retains its original tension up to around 1000rpm, with 10 degrees advance which was set statically. It will then start stretching and achieves full advance at 2500rpm.

I started with (A). Springs is loose and starts stretching immediately as the engine spins.

I then cut the spring and now at (C). The whole curve is slower, I could set it to full advance at 2500rpm but it would simply shift the whole (C) to the left, and my idle will still have over-advance.

With the shortened springs, its impossible to maintain F mark at 1000rpm, if I set full advance to 2500rpm.
I hope my understanding is correct.

[scottly]

forget the f mark,with the strobe increase rpm watching the timing advance,once it stops advancing set it between those two full advance marks,dont worry where it is at idle,once riding the bike itll be at full advance most of the time anyway.

Dave, his problem is that his advancer now doesn't reach full advance until 4000 RPM.
SOHCiro, the springs don't change the amount of advance, only the RPM. Either set it at the F mark at 1000 RPM, or the full advance marks at 4000+ RPM.

[madmtnmotors]

Seems like you understand the problem. From what you describe it does indeed sound like the springs are now too tight. How many miles on the bike? Sounds like the original springs could have been left alone. Yamiya sells new springs.

[SOHCiro]

-Scottly,
Yes, if you look at my drawing, you'll notice that the maximum advance is still the same regardless of the spring length. The only difference is the "rate" of advance (advance curve). By setting F mark at 0rpm(statically), I get 4000rpm full advance now. If I set it at 1000rpm, full advance will possibly be around 5000rpm.

-madmtnmotors,
It's got almost 60,000 miles. Honed the cylinders and changed the rings and all the top end seals a half year ago. Still have some compression loss, will be boring the cylinder next year. Yes, I now do think that I should have left the springs alone 

The problem now is that the plates adjustments can not compensate for the tightness of the spring. If I max out the advance, I could probably only get 3500rpm full advance.
I'll try stretching the spring, aiming for 2500rpm and see how it goes.

[scottly]

Base timing, regardless of rate, should be at the F mark. You may be able to slightly increase the lengths of the springs by squeezing the end coils into an oval shape with a pair of pliers, but a shortened spring will always be stiffer.
In your drawing, there should be straight lines from the 1000 RPM F point for all three curves, to the max advance RPM for each curve. Unless all three curves start from the same point, they are meaningless.

[SOHCiro]

-Scottly
That's right, there's no point in making the lines curvy, haha.
(A) and (C) start at 0rpm at F mark, simply because I set them statically. once the engine is running, it is no longer at F. I mentioned that idling at 1000rpm my bike is over-advanced, so it can't be at F mark.

I'm confused that some people swear by having max advance at 2,500rpm and leaving idle advance whatever.
Others say idle must be at F mark.

In my situation, accomplishing both is quite impossible. I'm making a trip to HomeDepot to pick up some wires. I'll try to replicate the original springs for under 5 bucks instead of spending over 50 for a set of tiny springs!

[scottly]

Ideally, the timing at 1000 RPM will be at the F mark, advance to the full advance marks by 2500-3000RPM, and return to the F mark when RPMs drop to 1000. If the springs are too weak, the advance will already start before 1000 RPM, so setting the timing at the F mark doesn't work.

[TwoTired]

Have the advancer flyweights been checked to ensure they move freely on their pivots?

[dave500]

forget the #$%*ing f mark!if your riding the bike properly itll be at full advance all the time,who cares what the timing is under 2500?set it to the full advance and be done with it,if your springs have been cut etc that's just stupid #$%* full stop !ditch the points and and use electronic anyway,ten billion other vehicles cant be wrong?

[PeWe]

This problem seems to be same as my CB750 had, too sloppy springs which will advance way too early. If setting ignition with that must retard a lot to not get it so advanced. It will not be able to advance much more. Your plate might have bad stoppers.

Take the advancer apart, check springs, end stop not advancing too much and lubricate it if rusty inside. I should tighten one spring. When mounting it on the engine,  check it's play before tighten the small 10mm M6 nut. Tighten it at max counterclockward position. (I have verified this on 2 different cranks and advancers with piston stop finding real TDC).
You will see that it will be easier to find correct setting now.
Here when I modified my springs: http://forums.sohc4.net/index.php?topic=131339.0

The way to set advancer found when I verified true TDC when timing the cam. I have tried with an alternative case mark for advancer at max clockwise position. This will not allow point plate to be turned enough clockwise ending up in too advanced ignition and run bad on low throttle lift.
Make sure that point plate will sit tight in case embosses. It is possible to hammer them a little to let them swell so plate will not go sideways when adjusting changing point gap and a never ending adjustment loop

Read these: https://www.motorcycleproject.com/text/sohcign.html
http://www.hondachopper.com/garage/carb_info/timing/timing1.html

[PeWe]

forget the #$%*ing f mark!if your riding the bike properly itll be at full advance all the time,who cares what the timing is under 2500?set it to the full advance and be done with it,if your springs have been cut etc that's just stupid #$%* full stop !ditch the points and and use electronic anyway,ten billion other vehicles cant be wrong?

If I should do that on my bike, it should run really bad with jerky take offs. I have adjusted my ignition to run really well from idle to high rpm. It is possible to adjust it properly, not difficult at all. I tightened my springs, full advance now at around 2600 rpm, not before.

Last rides this year was ignition and fuel screws adjustment making it run well from 2000 rpm on 5:th gear, twisting slowly and engine reacts really well, full at 3500 rpm and it reacts without any hesitations. If a little bit too advanced it will run bad before 3000 rpm, richer fuel screws will solve that but idle will stink and plugs get black.
Engine has 1005 cc, ported head, RC295 cam profile, Mikuni TMR32 carbs. TEC points with Hondaman ign module, Dyna 5 ohm coils. It has been a challenge to get it to run perfect.

Last 2 weeks of the season with knowledge of a little bit too advanced will make problems on low rpms that I earlier thought was carb jetting that never ended. I like to cruise on 5:th gear on very low rpm and just twist without gearing down, no sputter or hesitations as I have had before.

[Deltarider]

Whenever there's a problem with either not reaching full advance (or overreach for that matter) and/or plates not having enough adjusting room, step one is to check breakerpoints gaps are set correctly and if you did, to doublecheck for a possible mistake. Specify how you did it, because mistakes are easily made. Also any question about the ignition timing should be accompanied by informing us what ignition parts we're talking about, genuine Honda or aftermarket. My personal test showed that with genuine Honda parts (CB500), when breakerpoints gap is set exactly in the middle of the range prescribed by Honda, both static and advanced timing will be spot on, leaving enough adjusting room for some personal preference.
I myself don't like the idea of cutting springs, not before I have learned from more than one reliable source this is a 100% proven method. I'd rather have the situation where somebody undertakes the effort of producing new springs and then to the standard spring tension Honda specifies in the Shop Manuals.

[PeWe]

I check my point gaps with dwell meter to get the both equal. I had to increase gap to not get it too advanced. Root cause was the advancer play that force the advancer to sit correct as I wrote earlier.

I'm convinced that this is typical for CB750. The point plate is constructed to work with advancer in correct position, T lined up perfectly with case mark at true TDC as it will at max counterclockwise position. The play is rather much, around 4 crank degrees.
My first thought was my crank and advancer. Another crank (low mile from USA that passed APE on its way to me) and 2 versions of advancers show same thing.

[rotortiller]

I get 4000rpm full advance now. If I set it at 1000rpm, full advance will possibly be around 5000rpm.

 As mentioned by someone else: Full advance  occurrence  is RPM sensitive and will not change, the only thing that will change with timing adjustment is full advance timing mark reading. If you change the spring tension then yes the rpm point of full advance will be different. (Make sure the advance is free to move when fully installed with no binding) If the point gap is off  that will affect the the advance unit operational range on the points, you may want to experiment here as just because the gap is within spec does not mean you cannot tweak it within reason (spec guide range) to assist your situation.

[Bodi]

Seems to be a lot of confusion and misunderstanding.
The advancer has two basic specifications:
1 - total advance movement in degrees, from no advance to full advance. This is set by the advancer mechanism's movement limit and is only adjustable by modifying the weights or housing.
2 - advance vs RPM. This is basically a function of the weights and springs. The weights will want to move out when spinning, the springs hold them in. You can file weight off or change the spring tension to change the "advance curve" of RPM vs advance degrees.

So your basic description of what's happening does not make much sense. If you set the static timing at the F mark, the advanced timing will be some degrees ahead at full advance RPM. Fiddling with the springs will not make any change to the total advance, just what RPM it's reached at. Changing the static timing point to other then the F mark will not change the RPM range where advance happens.
The repeated advice here to set the timing with a strobe at full advance to the advance timing marks and accepting the resulting idle advance is wise. As long as the low RPM advance allows the engine to idle - not backfire or kick back when kickstarting (ouch!) - you're good. The engine should be at full advance for 99% of riding so full advance is the critical adjustment. Not enough full advance reduces horsepower. Too much full advance causes knocking and probably melted pistons eventually. Changing the springs so full advance is reached at a higher RPM just robs power below that RPM. Its not uncommon to adjust for a bit more full advance to get maximum performance knowing Honda allowed a safety margin for poor fuel etc. But it needs to be done carefully. If you dial in more advance knowing you only use premium fuel (some brands have ethanol free premium and owners of antique cars and bikes use it only to avoid the ethanol) then a fill with "regular" low octane fuel could be trouble.
There are very few cases where modifying the springs makes sense. If the springs are stretched out and loose at rest it's either due to a bad original tempering job (not unknown) or someone has heated them red hot (why?) and destroyed their temper... so get new springs: the stretched out ones have proven themselves defective and shortening them is not going to change that.
If the advancer's total advance is too much or too little you can possibly adjust it, making it more is pretty easy with a file but making it less is not so easy. Best would be a replacement used one as NOS ones are rare. The points cam shaft and the weights' "nubs" that engage it can wear and give a sloppy connection and this shows up as the timing jumping around particularly at idle, usually it's not a problem as total advance can be affected slightly but it won't cause a serious change.

[72 yellow]

This discussion reminds me of a thread from a while back about replacement springs from a company called Hillman Group.  The SKU #540356.  They are available from certain hardware stores.  Someone mentioned them, but never posted about how they worked.  They are supposed to be direct replacements for the stock springs.

[540nova]

Seems to be a lot of confusion and misunderstanding.
The advancer has two basic specifications:
1 - total advance movement in degrees, from no advance to full advance. This is set by the advancer mechanism's movement limit and is only adjustable by modifying the weights or housing.
2 - advance vs RPM. This is basically a function of the weights and springs. The weights will want to move out when spinning, the springs hold them in. You can file weight off or change the spring tension to change the "advance curve" of RPM vs advance degrees.

So your basic description of what's happening does not make much sense. If you set the static timing at the F mark, the advanced timing will be some degrees ahead at full advance RPM. Fiddling with the springs will not make any change to the total advance, just what RPM it's reached at. Changing the static timing point to other then the F mark will not change the RPM range where advance happens.
The repeated advice here to set the timing with a strobe at full advance to the advance timing marks and accepting the resulting idle advance is wise. As long as the low RPM advance allows the engine to idle - not backfire or kick back when kickstarting (ouch!) - you're good. The engine should be at full advance for 99% of riding so full advance is the critical adjustment. Not enough full advance reduces horsepower. Too much full advance causes knocking and probably melted pistons eventually. Changing the springs so full advance is reached at a higher RPM just robs power below that RPM. Its not uncommon to adjust for a bit more full advance to get maximum performance knowing Honda allowed a safety margin for poor fuel etc. But it needs to be done carefully. If you dial in more advance knowing you only use premium fuel (some brands have ethanol free premium and owners of antique cars and bikes use it only to avoid the ethanol) then a fill with "regular" low octane fuel could be trouble.
There are very few cases where modifying the springs makes sense. If the springs are stretched out and loose at rest it's either due to a bad original tempering job (not unknown) or someone has heated them red hot (why?) and destroyed their temper... so get new springs: the stretched out ones have proven themselves defective and shortening them is not going to change that.
If the advancer's total advance is too much or too little you can possibly adjust it, making it more is pretty easy with a file but making it less is not so easy. Best would be a replacement used one as NOS ones are rare. The points cam shaft and the weights' "nubs" that engage it can wear and give a sloppy connection and this shows up as the timing jumping around particularly at idle, usually it's not a problem as total advance can be affected slightly but it won't cause a serious change.

Disregard all previous posts and heed this.

Sent from my SM-G955U using Tapatalk

[SOHCiro]

Thank you all for your replies,
I'll shoot for 2500rpm full advance, and see where that takes me at idle!

-72 Yellow,
Indeed interesting. a quick google search did show an original article about the direct replacement spring, below link on page 56.
http://www.vjmc-florida.org/wp-content/uploads/2016/07/201702.pdf
Nothing comes up with "Hillman group SKU540356", but I'll be looking out for that and update if any local true value stores have em, and how they work.

[SOHCiro]

-Update:
I went to my local true value hardware store, actually called 2 of them and neither carried Hillman group springs.
I bought these made by "Century springs corps". 1/4" OD, Part number C-233. 2 long springs for 6 bucks.

I cut and shaped them to fit the advancer, they look great and works great. Decent quality at good price, especially considering the length they come in. I cut it 4 times to get it just the right length and still have more than half remaining.

After testing with timing light, It was too stiff, so I removed one spring and now gets F at 1000rpm, and full advance at around 2200-2700rpm, it's not spot on at 2500, it fluctuates quite a bit but I call it acceptable and runs better!
Only time will tell if these springs last agains the constant heat and tension, I'll provide more info in the coming months.

[PeWe]

Have you verified the point gaps?
Easiest with dwell meter when idling. You will hear when both points are eaqually set and see that they get same angles.
Another way is to set both with feeler gauge, decide one of them as reference and adjust the other one when idling. Without any dwell you'll not see which direction needed. I guess it will be easier if going larger a little bit and close until it sounds right.

When equal the engine will run much smoother. I'm convinced that people sync their carbs when points are not in sync. More gap will retard, less gap will advance the ignition
This might be the last fine adjustment!