Author Topic: 1948 t35.misfireing ?  (Read 6169 times)

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Offline george sutton

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1948 t35.misfireing ?
« on: 28 Oct 2009 at 15:38 »
 :frown: recently bought t35 mk1. always been owned by ldmcc members. restored two years ago, but only done 90 miles since. starts and idles nicely,but wont pick up on quick throttle, even dies.Have set up both carbs side by side on the bench with twist grip also. renewed cables, and ensured identicle movement. Always spits back only on o/s. renewed feed pipes with even and Level feed. Today  i set up an independant fuel supply to the o/s carb. The n/s fed from tank as normal, BUT,no, not on your nelly !tank and tap removed and cleaned,  thought to myself ,it MUST be the mag.  magneto was serviced on the restoration.  during fast idle I  can pull off each plug lead in turn and it will still run on the opposite cyl.ok.     BUT,try to open that throttle smartly and she gasps and spits back.  incidently, tappets set. magneto points and timing reset to the handbook, advance and retard cable checked and adjusted.  please what else can i do?? have i bought a rogue bike i ask myself?    Had one from new in 1949 ,lavished the same care on that one ,and she was a dream for 8 years. help please.

Offline eddie

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Re: 1948 t35.misfireing ?
« Reply #1 on: 28 Oct 2009 at 17:00 »
Hi George,
                 It sounds as if the carbs are a bit weak on the throttle cutaway. Try starting the bike and let it warm up, then try tickling the carbs to get a higher fuel level, and see if it responds better. If it does, then get some slides with a smaller cutaway. Incidentally, I have found that all the later Marks respond better with a 4/4 slide instead of the original 4/5. It is even more noticeable now that we have to put up with the dreaded unleaded. Also, I have heard that the 'super' unleaded has a higher viscosity, so tends to run weaker in engines that have carburettors rather than fuel injection (where a metered amount is pumped each time).
            Keep persevering,
                                         Regards,
                                                     Eddie.

Offline george sutton

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Re: 1948 t35.misfireing ?
« Reply #2 on: 29 Oct 2009 at 18:58 »
hi Eddie, warmed my t35 up today, and tried as you suggested to tickle the  offending o/s carb. , yes it DID seam to stop the weak symptom of 'spit back'. but then here i'm puzzeled, WHY does it only happen to the o/s carb. also changed the float bowls over, but still occurs only on the o/s when snapping open the throttle. There is deffinately no problem with fuel supply to both carbs.    your theory of unleaded to slide cutteraway ratio is logical enough, but then surely it would affect BOTH carbs, would it not? am going to try  a thin fibre washer between brass float jet and bowl top, hopefully to raise the fuel level !      anyway where could i get new slides for my carbs, which i beleave are the originals ?, regards george.

Offline Clive

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Re: 1948 t35.misfireing ?
« Reply #3 on: 29 Oct 2009 at 19:32 »
Hi George,
Try Hitchcocks Motorcycles Redditch Worcs for your Amal carb Parts
Regards
Cive

Offline eddie

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Re: 1948 t35.misfireing ?
« Reply #4 on: 29 Oct 2009 at 20:10 »
Hi George,
                 Presumably your carbs are used units, so the O/S carb could be more worn than the N/S, or maybe the slow running screw in one carb has been forced - so that one side is running weaker (even though the settings on both carbs are the same). You could try turning the slow running screws in slightly (giving a richer tickover) - this should improve the pick up.
              By the way, it is not a good idea to remove plug leads with the engine running - the mag is still generating sparks and if the gap is too great for it to jump, then it is likely to short across the windings, rendering the mag faulty.
                              Regards,
                                            Eddie.

Offline george sutton

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Re: 1948 t35.misfireing ?
« Reply #5 on: 30 Oct 2009 at 10:58 »
Hi George,
                 Presumably your carbs are used units, so the O/S carb could be more worn than the N/S, or maybe the slow running screw in one carb has been forced - so that one side is running weaker (even though the settings on both carbs are the same). You could try turning the slow running screws in slightly (giving a richer tickover) - this should improve the pick up.
              By the way, it is not a good idea to remove plug leads with the engine running - the mag is still generating sparks and if the gap is too great for it to jump, then it is likely to short across the windings, rendering the mag faulty.
                              Regards,
                                            Eddie.
thanks again Eddie, carbs were fully refurbished by Bratby no1. coachhouse works (staffs) only in aug. 08. including new needles and jets, slides matched to bores. Have tried all the adjustments you mentioned, also Hitchcocks ad. on tuneing.yes i know your right about plug leads, but one gets desperate. george

Offline Clive

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Re: 1948 t35.misfireing ?
« Reply #6 on: 30 Oct 2009 at 22:25 »
HI George,
Found these Factory settings hope this helps
Regards
Clive

« Last Edit: 02 Nov 2009 at 20:56 by Dave »

Offline george sutton

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Re: 1948 t35.misfireing ?
« Reply #7 on: 01 Nov 2009 at 18:00 »
well where are we in this saga of the cylinder that thinks its a blow lamp!.have used fresh fuel (95), have swapped plug leads, have even run it with leads direct on plugs with no cap.!! think i will donate it to NASSA, might give the next launch aboost.    looks like a head off job now, and valves out. Not bad this, is it, for a bike that had a 'Full restoration' less than two years ago !!   hurts abit after all the money Cotswold classics had out of me,   but i wont give up ! George. S.

Offline Clive

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Re: 1948 t35.misfireing ?
« Reply #8 on: 01 Nov 2009 at 19:26 »
Hi George,
Have a look at the Reference section on this site
Mark Series Maintenance Guide by John Holmes lots of good info on pistons and Cylinders.
Regards
Clive

Offline george sutton

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Re: 1948 t35.misfireing ?
« Reply #9 on: 02 Nov 2009 at 11:36 »
Hi George,
Have a look at the Reference section on this site
Mark Series Maintenance Guide by John Holmes lots of good info on pistons and Cylinders.
Regards
Clive         
Hi Clive,  well stone me, i had no idea such info was available on our webs, being new to computers at 76 i'm even more amazed!  have printed off the guide. trouble now is , i'll be awake all night digesting every word.  having bought this mk. when i was 17 in 1949, it was the very first m/c i ever took appart. (engineering apprentice) it ran beautifully for 8 years till i had to sell.  I never lost my love of the duggie.   Therefore that guide will refresh an old memory.   Many thanks Clive, your a brick,   in old english that means SOLID and dependable, dont know what it is in NZ.

 

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