UK Monster Owners Club Forum » .: Technical :. » Engines, Clutch, Gears » raising needle in carb found wrong jets ?? weird

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Old 11-09-2019, 07:08 PM   #1
jerry
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New M750, in carb found wrong jets ?? weird

this is weird delving into the poor low speed running of Bilbos ex M750 i found some anomalies in the carbs

OK according to parts book a 1997 Monster 750 should have

main jet 132.5
main air jet .70
pilot jet 42.5
needle jet Y4
jet needle 5C-J1 4th notch from top out of 6


what the BIKE actually has is

Main jet 128 ????????? clearly not correct !!!!!!!!!!
main air jet .70 correct
pilot jet 42.5 correct
needle jet unknown not gone that far yet
jet needle unknown no markings 3rd notch from top out of 6 & 1mm shim under




clearly something very amiss ??? 128 main jet cant be right even M600 had 132.5

bike defo running lean ,, could it be someone tried restricting it for learner ?? or are the jets from a M400 ??????


also where on needle might i find markings i have looked under a microscope and nought to see????



trying to decide what to do bike now has factory cans and airbox and filter back on

should i get some 132.5 main jets and then raise the needle a bit ?
i have some 140 jets and Sils and open air box etc could try them ??



your opinions please
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Old 11-09-2019, 08:15 PM   #2
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Think I’d be doing this:

https://rover.ebay.com/rover/0/0/0?m...2F283492962768
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Old 11-09-2019, 10:11 PM   #3
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or someone already has, but as flip suggests 40 quid to know where you’re at looks good to me

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Old 11-09-2019, 10:39 PM   #4
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Quote:
Originally Posted by Flip View Post
yes but thats a stage 2 kit for engine mods open pipes and airbox is it for 2 carbs or one ?? if its for 2 its good value
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Old 11-09-2019, 10:51 PM   #5
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Stage two is for open air box with a free flowing filter and/or less restrictive exhaust i.e. race cans.

Dynojet kits will always for the bike they intend to be fitted on so in this case for both carbs.

They usually have jet size options depending upon how you intend to run the bike, my 900 kit came with jet options, needles, shims and springs. Plus a template for cutting the air box lid and full set up instructions.

But unfortunately, as Slob has pointed out that listing has ended and the others on eBay are all full price at around £115
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Old 11-09-2019, 11:08 PM   #6
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Sent a photo of my carb bits to John in the States who tunes bikes for a living , we have identified my needles and they are tapered with no writing so they are definitely DYNOJET so are the springs ,,standard needle has writing and numbers on and not much taper at all ...

[He also says the 128 main jets may not be a Mikuni number as Dynojet put a number 128 in their stage 2 kit shim ??? so the jet could be a Dynojet part but what the size is no one knows

ITS weird we cant understand why these jets are in the bike ????? a mystery , 6 turns out is double what they should be . bike is so so lean the plugs are grey , I would love to chat with the owner before Bilbo

John has suggested that i refit the carbs with the 128 jet as it probably could be DYNOJET but raise the needle with the shims in and see if the bike runs richer and airscrews can be tirned in to about 3 turns out

if the bike is ok then leave it if not move needle again or add / subtract shim as required


and do plug chops as the plugs should not be gray but light brown , slightly rich is also OK

I can swop air box around as i have 3 different lids standard , part open and full open as well as some Sil open cans and standard paper , K&N or piper cross filters

I have 3 750 2v bikes to swop bits from and spares ha ha
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Old 11-09-2019, 11:27 PM   #7
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Jerry, Dynojet jet numbering is very different to Mikuni or Keihin and has no cross referencing (I would imagine your friend in the States would know this) so essentially the numbers you are reading have no bearing on what 'should' be in there if indeed the needles (and springs) are Dynojet items.

Have a look below, as to me what you have fitted sounds right for a M750 with a Stage One kit fitted.

Monster 750 Stage One:
http://www.dynojet.com/pdf/european/E7107.pdf

Monster 750 Stage Two:
http://www.dynojet.com/pdf/european/E7207.pdf

750SS Stage One:
http://www.dynojet.com/pdf/european/E7103.pdf

750SS Stage Two:
http://www.dynojet.com/pdf/european/E7203.pdf

Obviously doesn't explain why it is running so badly but hope that helps a bit- might be worth giving PDQ an email or call to see if they have any ideas on how to proceed?
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Old 12-09-2019, 01:53 AM   #8
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I have spent an hour going through the pile of receipts that came with a bundle for the bike and hey presto there is a receipt for fitting a stage 1 dynojet kit in 2015, looking up the reference its Dynojet 128 jets , new needles and springs , also fitted at that time was a pipercross air filter , and modified airbox cover ,, and a set of arrow exhausts , bike also had a session on a dyno ,

the arrows were not on the bike when sold to me

looking up the instructions for dynojet stage 1 kit i see that the needle spacer and shims have been assembled in wrong order??? the 3rd notch from top is correct by the kit but the bike is running lean at anything below 3500 rpm with standard cans or silmoto cans the only answer seems to be to raise the needle by one notch to 4th from top to richen it up and get the bike running with air screws at 3 1/2 turns and not the 6 they are at now , hopefully it will run better ...

with either the standard cans or the sils and one of the air box choices ,,

im glad i now know whats in the carbs ,, mystery settled ,, I hope now i can tune it to run nice between 1500 -3500 rpm without the lean glitches and lean grey spark plugs


It is also now clear that my older Monster 750 has a Stage 2 Dynojet kit in as that is the 148 jet number
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Old 12-09-2019, 09:27 PM   #9
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got itall back together and went for a run ,, its better at low revs round town not hunting or coughing so much ,, and its fine at all other times ,, I think i can improve it more ,, maybe another shim under the needle ,and some more airscrew adjustments ,
the spark plugs are nice brown colour

or maybe even raise the Float bowls but thats a bit drastic and very fiddly



however later in the day my mate pete decided to use his thermal laser to tune the bike , by meauring heat on engine cylinders and exhaust manifolds ,and fiddling with air screws , result was worse running ha ha
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Old 20-09-2019, 05:36 PM   #10
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This cant be right,


spark plug gaps on NGK Dpr8ea plugs are only 0.2m?????!!!!!!! jeeez i have set them to 0.6mm maybe the bike willrun right now ???
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