Author Topic: Mysterious (to me) power drop  (Read 5430 times)

Offline orabanda

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Re: Mysterious (to me) power drop
« Reply #60 on: 03.07. 2017 23:58 »
Have you checked the tank breather?

Online chaterlea25

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Re: Mysterious (to me) power drop
« Reply #61 on: 04.07. 2017 00:11 »
Hi Richard,
I seem to remember that the problem first arose on a fast run?
I dont like concentric carbs, but is 220 too small a main jet? Monobloc 260 according to haynes
Is the ignition timing the same on both cylinders?
Is there a worn or loose valve guide on the right hand side? (drawing in air)
I dont believe in the bias thingys

John
1961 Super Rocket
1963 RGS (ongoing)

Online Klaus

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Re: Mysterious (to me) power drop
« Reply #62 on: 04.07. 2017 09:55 »
Hi Richard,
I don't know the Concentric way, but this is not a Carb probem.
You have only one carb and this feed both cylinders. If one side is running hot this is definitly an ignition fault.
Have seen camrings with a difference about 6 degrees this means 12 at the crank.
I check all magnetos with a timing disc and the max deviation is 1,5 degrees at the camring.


cheers Klaus


If you think, everything is under control, you are not fast enought.

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Offline muskrat

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Re: Mysterious (to me) power drop
« Reply #63 on: 04.07. 2017 10:07 »
G'day Richard.
Just about time to junk those pistons. The hone marks in the bores are circular instead of crosshatch as the should be. She's getting hotter that side for sure but she's burning oil on both sides. Every time it nips the pistons get smaller and a hone makes the bore bigger resulting in excess clearance. The pistons rock and the rings won't bed in correctly. If it were mine I'd sleeve it back to std (just happen to have a pair of Hepolite sleeves you can have cheap).
I'd check all of John's suggestions and also check the combustion with a colourtune on both sides to see if you need a bias gasket. http://www.gunson.co.uk/product/G4074
220 main jet should be right in a concentric.
Cheers.
ps: my hands are never that clean!
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Offline RichardL

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Re: Mysterious (to me) power drop
« Reply #64 on: 20.08. 2017 04:16 »
Well, obviously I've been procrastinating the hell out of this and just moving slowly, not to mention actual serious matters that had to take precedence.

Back on July 3, I wrote this:

So, my plan is to give the lightest possible hone on the right side only, removing negligible diameter. Then, use my on-hand, half-a-set of 60-over rings. These rings came with the pistons some time ago, but I threw them over for some genuine Hepolite. I think it may be OK to be less choosy right now.

Assuming I don't get too much pushback on my "too lean" diagnosis and the rework of the bore and piston, I am left with the question of what to do about "too lean". Raise the needle on the concentric up from middle position? Change main jets up from (I think) 220? Add a bias gasket? All of the above? None of the above? Or. some mix of these?


I just finished reassembly after the light hone and new rings. I had also baked the head to test if the guides were loose. They were not. Went to look at the needle and found it in the top-most (most lean) position. I just goofed in the last carb rebuild. Don't know if this is the cause of the nip-up, but it's in the #2 position now. The bike started right up and a ride around the block was pretty spry. On the other hand, it was also quite smoky. I want to blame this on the new rings not bedded in, but maybe I have crossed the line on bores too big and pistons too small, like Muskrat has said.

I have to admit to doing just the minimum to get the top end back together and the bike on the road so I can attend and show in the show shown in the flyer. (I tried to use fewer "shows" but it was too much trouble.) If I show up with a smoking bike, so be it. It won't be smoking while just sitting on display. Please don't take this to mean I am ignoring all the good advice from everyone, It's just that I know I have a re-bore and pistons in the not-distant future, and that will be a good time undertake the careful timing evaluation. 

I'll let you know how things go tomorrow and if the smoke lets up.

Richard L.



Online Greybeard

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Re: Mysterious (to me) power drop
« Reply #65 on: 20.08. 2017 08:59 »
I was thinking, we haven't heard from RichardL for a while. I'm glad you are still extant.  *smile*

You'd expect to see smoke with new rings. Lets hope it settles down and you get some riding in before the winter.
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Offline RichardL

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Re: Mysterious (to me) power drop
« Reply #66 on: 20.08. 2017 15:02 »
OK, not taking the bike to the show. Smoke is the lesser problem. They say Confession is good for the soul, so here goes. One of the front rockerbox gaskets got out of place during assembly and she's leakin' like crazy. I'll still go to see the other bikes and answer embarrassing questions about where mine is.

Richard L.

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Re: Mysterious (to me) power drop
« Reply #67 on: 20.08. 2017 15:53 »
...One of the front rockerbox gaskets got out of place during assembly and she's leakin' like crazy....
Oh goody pushrod fun again!  *whistle*
Greybeard (Neil)
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Offline RichardL

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Re: Mysterious (to me) power drop
« Reply #68 on: 20.08. 2017 18:37 »
I'm going live from the Chicago Norton Owners' Club Bike Show at xx:50 after the hour from the time of this post. Go to ustream.com and search "rlai" without quotes. If you don't catch it live you can probably see it later. My bike is not here for the reasons already mentioned.

Richard L.

Offline RichardL

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Re: Mysterious (to me) power drop
« Reply #69 on: 04.09. 2017 17:29 »
OK, not taking the bike to the show. Smoke is the lesser problem. They say Confession is good for the soul, so here goes. One of the front rockerbox gaskets got out of place during assembly and she's leakin' like crazy. I'll still go to see the other bikes and answer embarrassing questions about where mine is.

Richard L.

Once again, the bike is back together after the now-long-ago nip up.  I am glad to report that smoke from the right side now seems (to me) about normal for an oversized, freshly-honed bore with new rings. It turned out that, when landing the barrels, I had broken the oil ring (as presumed by Muskrat in a PM chat). No real ride yet, but I'm temporarily happy.

Here are a couple of photos. The amazing thing to me was finding the shard of the ring on the floor under the bike after blowing air past the crankshaft to force bits it out the bottom.

Richard L.

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Re: Mysterious (to me) power drop
« Reply #70 on: 04.09. 2017 18:51 »
My fingers are crossed for you.  *good3*
Greybeard (Neil)
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Offline tinu

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Re: Mysterious (to me) power drop
« Reply #71 on: 29.10. 2017 19:48 »
It happened, that I tested last week, how it is to drive more than 60 mph / 100 km/h. The road was empty and long enough to get up to 75 mph. But I could not really get any faster, and when I turned back the throttle to slow down, the engine stopped, I almost fell off the horse... A few seconds later, everything was alright again.
Could this have had the same reason? First thought was more like Richard discribed in the first post, that there is not enough fuel in the carb. I have a monobloc mounted, and normally I open only one fuel tap...
Weather is wet and cold since then (except I am at work) so I could not repeat the test with both taps open...
What do you think on that?

Cheers Tinu
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