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T160 Jets

Home Forums TR3OC Members Forum T160 Jets

This topic contains 11 replies, has 4 voices, and was last updated by  Peter Hughes 4 weeks ago.

  • Author
  • #8598

    Peter Hughes

    Hi folks.

    T160 with Nova barrels. Base altitude 280m (920ft). Amal carbs, somewhat modified/improved, e.g. new floats; float height set; OK.  3 1/2 slides (changed out from 4).  Started on 170 main jets, too weak all through the needle range. Moved to 180s and mid setting. It’s still weak (on TS/DS, CTR OK), so I’ll raise the TS/DS slides to max rich, leave the CTR. On full bore plug-chop, the plugs are a little weak, but OK.

    It hesitates, particularly on inclines when not completely warm (and sometimes when it is). Fuel flow checked, seems OK.  Does anyone have experience of using even bigger jets than 180s on a T160/Nova barrels? Or, what could be wrong/what am I missing? Thanks, Peter

  • #8599

    David Lord

    Hi Peter

    What octane fuel are you using and at what revs in which gear do you get the hesitation?  Finally what exhaust system/silencers do you have?


  • #8600

    Peter Hughes

    Hi David,

    We still get 102 octane here in some (Aral) forecourts in Germany, use that as standard.  Hesitates at rev range 3,000 – 4,500 rpm in 5th gear, most evident on inclines. Much less evident on A-Bahn blast (4,500 – 6,000 rpm).

    Using lead replacement additive appears to have a very negative effect, unless it’s a coincidence.

    Standard pipes/collector box, standard black-cap exhausts. Should have mentioned: standard T160 air box (fitting that b****** is one of the banes of my life…), running with  K&N OEM replacement panel filter.

    Snapping throttle shut and then reopening appears to resolve the hesitation instantaneously, then it returns after 1-2 secs. The problem’s intermittent though.

    Another observation is that the problem may be cumulative; i.e. the longer the run, the worse it get. But that’s only evidence from one longer run a couple of weeks ago.

    Thanks for the support, Peter.

  • #8602

    David Lord

    The hesitation you describe usually indicates over-richness.  The problem with modern fuels is that the ideal plug colour is not the nice brown we liked to see decades ago.  The ideal colour looks weak (off-white) and I suspect that you are actually running too rich in an attempt to get a colour that isn’t white?  You are also probably under-revving if you are trying to get it accelerate at under 4000 rpm in 5th up an incline.  I take it dropping to 4th gets rid of the hesitation?

    I always found the best way to tune is to keep going weaker until it pinks and then back off a bit.  The attached Amal guide to tuning is really useful and if you use my method above instead of plug colour, you should get the result you want.

    You must be logged in to view attached files.
  • #8604

    Peter Hughes


    Thanks for the advice, interesting prognosis. Thanks also for the tuning guide and the Bushman’s guide.


    On the longer run the other day which involved a lot of hill work, the “hesitation” was very pronounced. I was worried, so stopped to investigate. The head appeared to have got very hot, such that I smelt fumes and observed some smoke coming off it. Guess the smoke was from the Loctite 564 that I’d used between head and rocker boxes a couple of months ago.


    Just for reference, I attach a couple of pics of the CTR and DS plugs (the CTR has the darker ground electrode). Bearing in mind your comments about modern fuels, how do these look to you?

    Thanks, Peter


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  • #8611

    David Lord

    As I say, I wouldn’t be guided by plug colour and take more notice of how the engine responds and sounds (although the RH plug in your picture does look sooty/rich).  I think you need to go back to the beginning i.e. do a WOT run to set the main jet (180 sounds too rich to me).  Then look at the responsiveness from very small throttle openings and change the cutaway if required (4 is the usual on a T160 with standard exhaust). Then do the mid range and set the needles (again I think you need to lean the needle setting to get rid of the hesitation)  If you change anything then re-check the other settings.  There is some overlap on all the settings, hence why you may need to go around it a couple of times.  The attached graph illustrates the point.

    I did fit an 850 barrel on a T160 once and as far as I remember it needed almost no change to the carb settings from standard.

    You must be logged in to view attached files.
  • #8616

    Peter Hughes


    Thanks for the response and reiteration. I’ll go back to the 160 mains  I still have,  see what happens and work back from there. Hope I don’t cook the head in the process!


    FYI: when it’s in a good mood, this bike currently pulls exceptionally well from around 2,000 rpm right up to 7,000 – as far as I’ve dared take it so far.

    • #8743

      nigel wheatley

      i agree you’re far too rich, the only real change you’ve made is the big bore kit but you are still on standard air box and exhausts. On that set-up, I would only try one size above standard on your main jets – you may not even need that! and go back to No4 slides

      Alternatively why not fit some peashooter (norton commando style) exhausts, that might help it breathe better but even then I think it will be too rich

  • #8758

    Peter Hughes

    Thanks Nigel. Have gone back to 170 mains, needle at weakest. Bags of power 1/2-full, pinks on 1/8 – 1/4 throttle, but only after 20 miles or so. Maybe raise the needle one notch?

  • #8804

    nigel wheatley

    It could easily take 15 or 20 miles for a trident engine to warm-up fully. Check your ignition timing on a strobe first.

  • #8805

    Frank Long

    I don’t have Nova barrels on my T160 but I did port (gas flow) the head and use larger intake valves.  I use K&N intake filters (not the stock black airbox filter housing) and stock blackcap exhausts.  It took me forever to tune anywhere near properly.  However, some things helped.

    With this increase in air demand from the larger displacement, try using 2 line needles instead of the weaker 5 line stock T160 ones placed at leanest position (top ring).  Phil Pick has mentioned this in our club Service Notes with regard to a highly modified stock displacement T160.

    From the photos of the plugs, they are running rich but I can’t tell at which carburetor range this is happening.  If this is a full throttle chop reading on new plugs, they are rich.  However, if these are representative of how the plugs look after a general run, then who knows at what range the carbs are rich?  Further, there are specks on the insulator and small silver reflective balls of metal seen on the plugs – detonation.  Gauging from the annealing point on the ground strap of the plugs, the heat range of the plug is  slightly warm.  Champion N2C  ( or equivalent heat range in other brands) might be worth a try.

    The Amal-carb-Info document is good to remember.  Primarily, it tells you that the main jet influence is NOT just the upper 25% of the throttle range like so many Amal tuning instructions state  but extends at least down to  half throttle.  I took me a long time to figure that out.  When I was tuning my bike, I even tried 220 main jets and the bike ran well.  By the time I was finished, 190 mains are what I now run and the exhaust is just starting to color from heat.  So no, you should try bigger main jets then the 180.

    What I did:  bought mains from 160 to 220 to test.  Used 2 stripe needle at leanest position, made a .1055 needle jet and made a 3 3/4 throttle slide.  Champion N2C plugs.

    What you should try :  .106 needle jet, 3 1/2 slide, 2 ring needle at leanest position and start with 220 main jets and work down to smaller jets if needed.

    I personally believe that your  richness is from richness in lower throttle openings (which is why I leaned out my needle jet to .1055 and slide to 3 3/4) and that the detonation is from higher throttle settings.

    All this assumes stock timing and high test fuel.


  • #8821

    Peter Hughes

    Dear All, thank you for all your feedback. Work in progress at this end. Currently at mid-upper throttle settings – 170 main, 106 needle jet, needle pos. 2 (second weakest), all appears well.

    Currently slide 3 on the cut-out. Tickover at under 1,000rpm OK, picks up from there with the occasional small hiccup. Tickover markedly slower after the bike has been left for a few minutes.

    I’ll take on-board all your valuable feedback, changing jets/cut-outs around one item at a time and keep you posted.

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