Miss high rpm

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Model T Ford Forum: Forum 2015: Miss high rpm
Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Sunday, December 20, 2015 - 01:51 pm:

At idle on mag or bat it runs smooth but at higher rpm it seems run rough or slight miss.
NH carb seems very touchy 1/4 turn from to rich black smoke to to lean it won't runthe coils are rebuilt and have spares no differance
The anderson timer (new) as is the brush
X plugs
I'm leaning towards carburetor I have bead basted it and soaked in cleaner
Engine new rebuilt but plugs a red black with carbon


Top of pagePrevious messageNext messageBottom of page Link to this message  By G.R.Cheshire on Sunday, December 20, 2015 - 01:59 pm:

Red with black carbon sounds like rust. Have you done a pressure check to see if the head gasket is bad? At low idle a minor leak would not affect much, but at higher RPM's greater pressure (and vacuum)could bring in more coolant causing the miss.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, December 20, 2015 - 03:03 pm:

Sounds like the main jet and / or needle are worn out so you have a carburetor that is not metering fuel properly. Or maybe the float is set too high? The symptoms are the same for either of those faults.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Sunday, December 20, 2015 - 03:35 pm:

What Royce said. Either worn out of a broken off tip. Also believe you're in for a re-build with a good rodding out of the passages too.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Dimock, Newfields NH, USA on Sunday, December 20, 2015 - 04:00 pm:

Bob. The title sounds like the name of an unlimited hydroplane. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Sunday, December 20, 2015 - 04:06 pm:

OR a broken off tip. Sorry


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis Seth - Ohio on Sunday, December 20, 2015 - 05:37 pm:

Here is "Miss High RPM"


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Stroud on Sunday, December 20, 2015 - 06:28 pm:

Sister to Mrs. Low End Torque? Sorry, I couldn't help myself. Dave


Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Sunday, December 20, 2015 - 08:17 pm:

I have print her for the shop wall pinups
Motor is freshly done new copper head gasket only thing I didn't do is mill the head. I checked it and appeared to be ok.
The main needle has a nice tip but unsure of the seat I'm going to go through the carb again and barrow a known good one and try it.
If no change I'm going pull the head and mill it block been decked


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Sunday, December 20, 2015 - 08:45 pm:

Bob
Suggest you try another timer before you pull the head.
Many high speed missing issues are timer related.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Sunday, December 20, 2015 - 09:13 pm:

Ron I only have an old one but easy thing to try
Pulling the head is my last resort.
The black carbon what has me leaning towards the carb as you should be able to lean it out enouf burn it off , at least I been able to befor


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Sunday, December 20, 2015 - 10:22 pm:

Bob
My suggestion assumes you fix the narrow range mixture control issue. Having fixed that I would pursue the timer.
Ron


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Harper - Keene, NH on Monday, December 21, 2015 - 12:56 am:

Hi Bob.
What gap do you have on your X plugs?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard E Moore Jr. Pickwick lake Tenn. on Monday, December 21, 2015 - 07:29 am:

I'm with Ron. I just went through this. The timer had ridges on the contacts. Only missed at speed. Changed the timer and couldn't believe the difference. I thought I hand a bit of an engine rattle but that left along with the engine miss. I need to listen to KGB more often. The biggest improvement though was changing over to the NH Holly. Learn something every day.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Verne Shirk on Monday, December 21, 2015 - 08:00 am:

All of the ideas expressed about the carb, timer, spark plugs, etc. If you go through all of those and still have a problem, I would not rule out the coils. They are "rebuilt" but that can mean a lot of different things to different people. I've had them run OK at idle or even above but miss out at high speed. 99% or all fuel related problems are ignition and vice-versa. Just some thoughts anyway.

Verne Shirk
Wichita, KS


Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Monday, December 21, 2015 - 11:43 pm:

Gap is .030 tried at .025 and .035 with no change
Plugs are old and will try another set
Coils rebuilt but sat on self few years I have two sets and Ron P doing another set soon
Only thing new to me is the high compression pistons
I never run them befor
I got new rings as I stated new rebiulders and will do a compression test once I go fetch the gauge from my dad over Xmas visit


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