Tuning issue 336, Dellortos, dual plugs

[R90SS/6]

Bike: 1975 R90/6
Cam:336 (6 degree advanced been can type)
Carbs: 38mm Dellortos (R90S jetting except for richer #65 idle jet)
Pistons/Cylinders: (Siebenrock 9.5:1 1000cc pistons with Nikasil Barrels) New
Heads are rebuilt with later rocker gear and dual plugging.
Ignition is a crank mounted Omega. timing set at 3 degrees advance with 28 degrees full advance.

I just put 300 miles on the bike since making all the modifications.
For the fist 150 miles of breaking in the bike ran amazingly well with lots of smooth torque throughout the range.
Since then I've noticed a drop in power over 4500 rpm and cutting out at full throttle.
To try and remedy the problem I......
I replaced the floats and adjusted the bowl levels.
Adjusted and equalized the throttle pumps.
Balanced the carbs
tried richer and leaner main jets
tried advancing and retarding final advance
New plugs

Compression is 140 psi on both sides.
Leakdown test shows only 2-3% leakage, none on valves.

I'm sure if I keep tweeking it I'll eventually find what's going on, but right now I want to ride.

Any ideas?

[CycleDoc59]

Originally Posted by R90SS/6

Bike: 1975 R90/6
Cam:336 (6 degree advanced been can type)
Carbs: 38mm Dellortos (R90S jetting except for richer #65 idle jet)
Pistons/Cylinders: (Siebenrock 9.5:1 1000cc pistons with Nikasil Barrels) New
Heads are rebuilt with later rocker gear and dual plugging.
Ignition is a crank mounted Omega. timing set at 3 degrees advance with 28 degrees full advance.

I just put 300 miles on the bike since making all the modifications.
For the fist 150 miles of breaking in the bike ran amazingly well with lots of smooth torque throughout the range.
Since then I've noticed a drop in power over 4500 rpm and cutting out at full throttle.
To try and remedy the problem I......
I replaced the floats and adjusted the bowl levels.
Adjusted and equalized the throttle pumps.
Balanced the carbs
tried richer and leaner main jets
tried advancing and retarding final advance
New plugs

Compression is 140 psi on both sides.
Leakdown test shows only 2-3% leakage, none on valves.

I'm sure if I keep tweeking it I'll eventually find what's going on, but right now I want to ride.

Any ideas?

Ignition settings sound correct. Have the valve settings been checked after those miles? They
tend to change fairly soon right after a rebuild... Do you have good voltage/charging numbers? The
original voltage regulator cut too soon, resulting in a chronically undercharged battery; and the coils don't
like low voltage. And the current load is higher now with dual-tower coils.

If it seems to be a miss-firing problem, a somewhat messy diagnostic is to tape a timing light on
the gas tank, go ride, and move the pickup from one cylinder to another...... I found a bad coil wire end in a dual
coil bike with that method last year.

[R90SS/6]

Originally Posted by CycleDoc59

Ignition settings sound correct. Have the valve settings been checked after those miles? They
tend to change fairly soon right after a rebuild... Do you have good voltage/charging numbers? The
original voltage regulator cut too soon, resulting in a chronically undercharged battery; and the coils don't
like low voltage. And the current load is higher now with dual-tower coils.

If it seems to be a miss-firing problem, a somewhat messy diagnostic is to tape a timing light on
the gas tank, go ride, and move the pickup from one cylinder to another...... I found a bad coil wire end in a dual
coil bike with that method last year.

Yes the valves have been reset a few times already. I'm using a Ducati style Enduralast Alternator, should be plenty of juice. I'll run a check on it though. Plug wires are new but the Dyna grey coils are used. I had not thought to check those, I've been so sure there was a carb or timing issue. Thanks

[ericrat]

Perhaps a fuel flow issue? That bike should just be waking up at 4k. Snowbum says flow should be better than 350cc (~12 ounces) per minute. Could be clogged petcock/filter etc.

I see you replaced the floats, but a low float level could be a cause too.

Good luck,

Eric

[craydds]

I offer no solutions for your issue, but you mentioned you have the Enduralast alternator. I am installing one on my '75 R90S and have some wiring questions. Perhaps you can help me. See my recent post, "Enduralast on R90S".

[R90SS/6]

Originally Posted by ericrat

Perhaps a fuel flow issue? That bike should just be waking up at 4k. Snowbum says flow should be better than 350cc (~12 ounces) per minute. Could be clogged petcock/filter etc.

I see you replaced the floats, but a low float level could be a cause too.

Good luck,

Eric

The ignition and charging system checked out fine. It appears that it was a fuel flow issue. Never had a problem with the 308 cam, but with the 336 and extra cc's... it wants more at full throttle and float levels are more critical. The floats were set a millimeter or so too low. I had followed Sno Bum's http://www.bmwmotorcycletech.info/dell.htm directions and set the floats so that 55cc's of fuel would drain out. This put the floats too low. Maybe the newer Dels (like the ones I have) hold more fuel in the bowls. When I moved them up to the exact Dellorto spec (I had to build a tool to measure it exactly) of 18mm http://www.ducatimeccanica.com/float_levels.html the full throttle starvation problem went away and even the idle improved. I'm really not sure why it worked fine for the first 150 miles of break in. Maybe compression increased as the rings set in and changed the fuel requirement. Any theories?
Question: They make needle and seat sets that flow more volume into the float bowl faster http://shop.bevelheaven.com/detail.aspx?ID=474. I'm using the stock R90S Needle valve http://shop.bevelheaven.com/detail.aspx?ID=59. Since the floats control the fuel level, why wouldn't I want the largest flow volume possible? Why wouldn't any bike regardless of the fuel requirement?

[craydds]

Flowing more fuel is no problem since, as you mentioned, fuel level is controlled by the floats. I am sure the stock Dellorto R90S needle/seat flows adequately, but nothing wrong with more flow, and I'll bet the high flow set cost is cheap. Sounds like you've solved your fuel starvation problem by increasing the fuel level in the bowls (so ignore my previous response).

[supershaft]

I was going to guess ignition.

I would run more ignition at idle. 6 to 28. It makes a pretty big diff down low.

I never had a fuel starvation issue with my 1000cc/Dell's/336 and stuff but I just set the floats per Dellorto. I don't pay much attention to snowbum. So much of his advise doesn't work well if at all. Don't get me wrong, I do look up stuff there too but . . . . 12 ounces per minute? What on earth for? That would keep a 450hp Pratt and Whitney R985 happy and they burn about 25 gallons per hour putting along cranking out around 1000ftlb of torque.

I started out with stock R90S jetting and gained a lot of power rejetting.

I ended up with 62 pilot jets, disconnected accelerator pumps, 1mm richer slides, K9 jet needles, 262 needle jets and 130 mains. Compared to stock R90S jetting, that got me a lot more power from low midrange on up to over 8000rpm and into over rev. I don't recommend revving them that high without titanium valve spring retainers.

Good luck!

[ericrat]

Originally Posted by supershaft

I don't pay much attention to snowbum. So much of his advise doesn't work well if at all. Don't get me wrong, I do look up stuff there too but . . . . 12 ounces per minute? What on earth for? That would keep a 450hp Pratt and Whitney R985 happy and they burn about 25 gallons per hour putting along cranking out around 1000ftlb of torque.

Good luck!

It sure seems like a lot of fuel when I accidentally know off/pull a fuel line and it is spreading across the garage floor.

12 oz per minute = 12 * 60 = 720oz/hour or 5.5 gallons per hour. That doesn't seem out of line.

I don't know aircraft engines, but those number seems right, 1000ft/lbs at about 2200 rpm is around 450HP, not exactly putting around though. 25 gallons of fuel comes to about .3 BSFC, that sounds too good to be true. Must be putting out more like 350HP "putting around".

An airhead making 70HP sustained, would need about 5.8 gallons of fuel, funny 'bums number is pretty good. .5lbs of fuel = 70HP/35lbs-gas. 35lbs-gas / 6 pounds per gallon is 5.8.

I am not trying give you a hard time SuperShaft, but I knew that your maths didn't look right. These numbers are all a little theoretical since the time unit is hours and we don't (typically )run 70HP output an hour sustained.

I just checked my R100 and it is delivering about 20oz/minute on a full tank.

Shaft is right about that not being enough advance down low, but that is the best your can do with the Omega to get at the 28 degrees total. To my mind Omega threw away a lot of options on the 42-47 degree range that we could have used on the other end.

Glad you are running better now,

Eric

[supershaft]

Busted! Sorry ericrat and everybody else out there about the fuel flow!! For some stupid reason I was thinking in pounds! I am so use to catching snowbum out that I dreamed this one up. My advise about his advise still stands AFAIAC. Overall, there is advise out there that you have to have both petcocks on and whatnot when most of it just isn't so.

Thanks for catching me out and not going for personal blood. It says a lot!

[supershaft]

I forgot to add that I use to work on small radials. Mostly Wrights and Warners but more are familiar with P+W R985's. I only worked on those a couple of times really. One of my bosses had one in his G17 Staggerwing. That plane was bad to the bone!

[R90SS/6]

Originally Posted by supershaft

I was going to guess ignition.

I would run more ignition at idle. 6 to 28. It makes a pretty big diff down low.

I never had a fuel starvation issue with my 1000cc/Dell's/336 and stuff but I just set the floats per Dellorto. I don't pay much attention to snowbum. So much of his advise doesn't work well if at all. Don't get me wrong, I do look up stuff there too but . . . . 12 ounces per minute? What on earth for? That would keep a 450hp Pratt and Whitney R985 happy and they burn about 25 gallons per hour putting along cranking out around 1000ftlb of torque.

I started out with stock R90S jetting and gained a lot of power rejetting.

I ended up with 62 pilot jets, disconnected accelerator pumps, 1mm richer slides, K9 jet needles, 262 needle jets and 130 mains. Compared to stock R90S jetting, that got me a lot more power from low midrange on up to over 8000rpm and into over rev. I don't recommend revving them that high without titanium valve spring retainers.

Good luck!

Down low, and transition from idle to full RPM are actually really good. No flat spot, revs really fast. I'm attributing that to the 6 degrees advanced cam (later bean can style 336) and of course to the post 1981 clutch/"fly wheel". I've got the titanium retainers and new springs shimmed to 36mm..... but I'm trying not to over rev it until I've got at least a thousand miles on it. This is proving to be difficult, I guess I'm going with the hard break in philosophy.
It definately likes the floats up at 18mm. Idle and top end have improved, but not perfect. At idle I'm having difficulty keeping the idle speed down. I'm running #65 jets the rest is all R90S. I've got the carbs all ballanced, but after I go for a ride it will suddenly be idleing at 2000 rpm. There's plenty of play in the cables (throttle and chokes). When I try to tweek the idle speed down the idle drops off suddenly. After some time I can get it ballanced at 1000 rpm again, but after a ride it goes back up to 2000. I may have a leak in the choke assemblies or the Omega ignition is set to advance to soon, I don't want to use richer idle jets because the screws seem just right at 1 1/2 to1 3/4 turns out.
The other issue is at full throttle. The missing has gone away with the float adjustment, but It still seems a little flat under load at or above 4500. Not bad, but not as good as I had it. I wondering about adjusting the advance. With the bike set at 6 at idle and 28 at full, I end up with such a short, quick, curve. I've been following Dr. Curves article http://mailer.fsu.edu/~jroche/road_rod.html and he suggests that full advance should be around 6000rpm for dual plug bikes. Unfortunately, since I don't have bob weights I can't slow the curve down...Not sure if it's possible to get full advance at that high an RPM without retarding idle further. I definately need to play with the curves and timing more before I do anymore rejetting. I'm going to cut a hole in the front cover so I can change the settings easily and plug it with a rubber timing plug.

[Middleweightboxer]

My wife built a R90S quite similar to what you are describing except for the charging/ignition systems. I tried every ignition timing combination that I could find and none worked for this bike. Some were just wrong.

Through experimentation I ended up with idle timing set at the S mark. This is the only setting that would allow the bike to idle properly. Forgive me I don't remember the advance timing numbers but it was necessary to limit the full advance after dual plugging. With two flame fronts you can't use all the advance that a single plug setup uses. The burn is happening faster.

I machined shims to limit the total advance on the mechanical advance unit. We would get detonation at the stock full advance timing. In addition, I find that with the crap we have to use for gasoline these days, my stock engines are happier with a little less advance.

So if your running anywhere near the stock full advance try backing it off. We have run her bike hard for over 40k miles now and it runs perfect.

[supershaft]

Make sure your new carb spigots aren't leaking air after the engine gets good and hot.

I suspect you might need the mixture screws richened (out) a bit more and a bit lower idle speed.

Make sure your new valves aren't leaking with a leak down tester. It has happened to the best of them and it happens all the time to others.


I suspect that 6000 rpm full advance was a typo but I have never asked him. I don't see it helping. I think I remember some people waiting until 4000 or 4500 for full advance? Personally, I don't like the timing options on most aftermarket ignitions. There is one from Germany that I like but I can't remember the name of it right now.

Flat on top? R90S 155 mains are way too rich but so are the pumps! You have got some serious free hp coming your way when you get those things mixing right. Rich on top is a real power killer!

[Beemerboff]

My G/S goes around 260 miles on 5.8 gallons, never managed to use that in an hour yet, but I will keep trying.

A few years back I had a car with a fuel flow gauge on the dash, and this demonstrated the wide variation in fuel requirements depending on the throttle position, etc.

So if you did indeed have an engine which averaged 5.8 gallons over an hour you would a maximum flow of 3/4 times that to cope with the peak flows. As someone has already said.

I wasn't impressed with the Omega on my R100GS, made no improvement to the way the bike ran and couldn't cope with the Oz heat.

Dont know the resistance of the Grey Dyna coil but I was running one Brown one.

Replaced the Omega with a Boyer Micro power which comes with a matching coil and still costs less than the Omega.

It only has one curve, but as that seems to be the right on I dont need any more.