Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Engine pounding ?

Engine pounding ?

Moderators: Curt!, Pa

Post Sun Jul 14, 2013 3:24 am

Posts: 16
Have a stange new thing start hapening this week.. :(

When i´m driving above 30 miles/h speeds and give it to much trotel the Engine starts pounding,
:shock: Whene i ease the trotel it disapers. when i use the trotel slowly and easy= no problems

feels like mix is to leen... i`ve tried to upp and down on main, pilot and nedle, but no diffrence..

Have i destroyed the bearings allready?? I know that mainshaft bearings there set upp i bit lose..

Anybody recognice this? :oops:

Engine is a new build: 4 7/16 stroker, mikuni 34, std cams, 5 alu heads, comp is about 6:1 , 85 psi

Have had some problems with jetting the mikuni, now it is : 200 main, 30 pilot, 6dh4 nedle,


Post Sun Jul 14, 2013 11:01 am
Pa Site Admin

Posts: 5551
Location: Ohio USA

This is just an educated quess on my part but I thing the bearing are set to loose.

Post Sun Jul 14, 2013 2:18 pm

Posts: 745
Location: Pa. , USA
Not clear on the pounding definition, could it be pre ignition engine knock or is it more profound ?
Vintage roadracing, Class C, AHRMA # 335

Post Mon Jul 15, 2013 10:27 am

Posts: 536
Location: Wa, USA
My 45 used to make a similar noise when the transmission mounting bolts came loose.

Post Tue Jul 30, 2013 2:38 am

Posts: 16
Sorry about the slow reply. Been away on from home and didnt internett.

Engine pounding? Or maby Nocking i might say.. :?
Gearbox and trans is firm and ok..

I think i might have found the problem :cry: adjustment of carb and ignition

Just got the manual from "victory mikuni vm tuning"
It spred some light in the darknes.
Folowed the instruktions and:

The needle jet is to big :oops:
So i put the needle on max lean and lowered the flowt hight
I got better but mid-range is still way to fat.
Ordered some parts..

New question :?:
Sould the ignition be full retadred or full advanced when
Adjustin the ignitniton buy the book.
Dont realy anderstand what they mean in the book...


Post Wed Jul 31, 2013 4:31 pm

Posts: 366
Location: Bergen, Norway
To adjust the air and idle screws I have had best results setting the ingnition fully retarded.


Post Wed Jul 31, 2013 9:23 pm

Posts: 386
To adjust the IGNITION,
First adjust the points gap on the highest point of the points cam. Easiest to do it on the wide lobe. Set at .022.
After the points gap is correct, set the ignition timing.
The timer needs to be FULLY ADVANCED.
Set the timer so the points just begin to break open as the timer hits the full advance stop on the compression stroke of the FRONT cylinder with the timing mark centered in the hole. Do this by rotating the timer base, do not change the points setting.

Post Thu Aug 01, 2013 3:33 pm

Posts: 366
Location: Bergen, Norway
Ooops. Rubone. You're right.
I answered a question Rob did not ask.


Post Thu Aug 01, 2013 4:32 pm

Posts: 366
Location: Bergen, Norway
It would be interesting to know the final jetting once you get there.

My next stroker is in the pipeline and I'm considering using a 34mm Mikuni on that one.
When doing the stroker i have now I got a 36mm. After jetting i realised I needed to play with the low speed circuits to get it at it's best. Doing 120km/hours I still only have a little over 1/4 throttle. Main Jet is not into play at that throttle opening...


Post Fri Aug 02, 2013 5:28 am

Posts: 16
Tanks for info :D
I have adjuster ingition now (buy the book).
Runns nice and good up to 1/3 throttle.

one thing.. when letting go of the throttle in speeds around 30 mils/h (3:rd gear) im getting bangs from the muffler :(
Is it still the ignition or the needle-jet thats is to big :?:

Yes i will let you know, i;m actuali following the guidlines from the victory Book..

Post Fri Aug 02, 2013 6:55 pm

Posts: 159
Manifold leak.

Post Tue Aug 13, 2013 4:03 am

Posts: 16

My settins for the moment, only tested it for a short time.
Bike runs much better then before, main problem was the jet needle.
Have not tryed whit 159 p6 or 6dh3.

Jet needle 159 p4
neddle 6dh4 on third clip
air jet 1.0
main 260
pilot 3.0

Post Sun Aug 18, 2013 3:39 pm

Posts: 366
Location: Bergen, Norway
Robban. Thanks. I did not fully understand. Did you change the needle jet from P-6 to P-4?

Post Tue Aug 20, 2013 5:11 am

Posts: 16
I was Q-2 needle jet orginal setting that came whit the carb.
Will test whit P-6 later this week.

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