Carb jetting confusion... are jets this small common?

[benjamin freeman]

ok so short background summary, 1985 vmax was running fine then sat for a few months and now it will start but it will only run on choke and the idle is erratic(revving and slowing on its own). so i figured i let it sit too long and its in need of a good carb cleaning. simple enough right? well i got the carbs off and started pulling jets to find out that all but one of my jets is WAY too small(according to the manual).

stock jets sizes are as follows:
37.5
90
170
152.5

the jets i found in my carb:
37.5(only jet that was correct/stock size)
80
150
137.5( this is the main jet and ridiculously undersized IMO)

as you can see all jets are undersized except the stock pilot jet, and the main jet is almost comically undersized. the bike was bought in phoenix Arizona so there is no reason for high altitude jetting. On top of all that the bike came with aftermarket slip on exhaust(not sure of the brand there is no markings) and a K&N air filter which mostly people recommend increasing jetting, which makes me even more confused!

as i said before the bike seemingly ran fine before sitting with no popping or power issue's with these jet settings(that i could tell! it still seemed pretty damn quick to me but its my first max so i cant be 100%) and im not sure how that was possible. i plan on returning the jets to stock settings with the jets in my rebuild kit but i was really curious to get some thoughts from more experienced vmax owners.

so in conclusion my real questions pretty much are just 3 things:
1. has anyone seen jet sizes this small used on vmax before
2. how was it running fine with these settings
3. does anyone foresee any issues or problems arising from returning the bike to stock settings

thank you very much for your time and i hope everyone is having a wonderful day!

 

[Fire-medic]

I'd use 150 or 147.5 Mikuni mains & go OEM for the others. Get a couple pics of the exhaust and measure one of your front header pipes for outer diameter. Do you have the stock vanity covers over the header to exhaust port area? Confirming the header outer diameter size will help us to see if you have OEM header pipes. If you have the exhaust port to header pipe vanity covers, the likelihood is your exhaust headers are OEM. An outer diameter measurement should confirm that.

 

[benjamin freeman]

I'd use 150 or 147.5 Mikuni mains & go OEM for the others. Get a couple pics of the exhaust and measure one of your front header pipes for outer diameter. Do you have the stock vanity covers over the header to exhaust port area? Confirming the header outer diameter size will help us to see if you have OEM header pipes. If you have the exhaust port to header pipe vanity covers, the likelihood is your exhaust headers are OEM. An outer diameter measurement should confirm that.

Ok so from the looks of things I believe the headers to be stock but i will leave that up to you. the headers measure 47mm/1.850 at about 6 inches down from the exhaust port and 35mm/1.377 at the slip on connection I have included pictures of front and rear headers, plus underside connections and included a pic of my slips on's just in case.

 

[maleko89]

Stock header pipes. Nots sure what the mufflers are.

 

[Fire-medic]

Stock header pipes. Nots sure what the mufflers are.

Agreed.

 

[one2dmax]

Appears to be Cobra's with the stock pipes (and the worst performing system you can get). AND, you did not mention of they are Mikuni jets or DJ jets (or another brand). With the Cobra's it's not likely way too small though maybe a size or two smaller then I would normally suggest to go down to.

 

[MaxMidnight]

Sean makes a good point about the jet manufacturer but we know that DJ sizes are numerically higher than the equivalent Mikuni so may not be a consideration.

If the bike was running well before your problem and a plug chop shows the mixture to be OK then IMO if it ain't broke don't fix it.

We can all guess at what the correct jet size is and it may benefit from a little tweaking. You can try swapping jets around but that involves time and money.
It also depends on your ability to discern any differences (in insult intended).
I would save time and probably money by getting a dyno base line run. That way any changes you make will be based on factual data not guesswork or opinion.

 

[dannymax]

Rule of thumb...if you didn't re-jet to make it run bad then you don't need to re-jet to make it run better.
So...what did you do? You let the bike sit for a few weeks. What is the normal result from that? Dirt, scale, evaporated gas residue...in other words, dirty carbs.
Solution - clean the carbs and fuel delivery system.

And while you're at it clean all the points of contact in the spark plug wire, plug cap, coils also.

 

[benjamin freeman]

sorry it took me a minute to get back to respond because ive actually been dealing with a whole new problem since then so i just forgot. so after i got all my parts to come in i was waiting for i rebuilt the carbs returned it to factory settings and jets and the bike runs like a champ. BUT after a my first couple rides i noticed the bike really didnt like to start when hot the starter barely cranked like the battery was dead even though it was perfect. i know the old 2 brush started are a common hot starting issues so i go to replace and broke a damn old rusty bolt head off my thermostat housing during the process of changing that starter and have been dealing with the giant pain in the ass the broken bolt has presented ever since and kinda forgot to get back to respond to the carb thread. so in conclusion to the original post a good rebuild and return to factory setting worked fine and fixed on my running issues, but now i have entirely new problems that i will probly make a new thread for later tonight. thanks to everyone who posted and provided help/info.

 

[Fire-medic]

Can you weld a nut to it? Or a slightly-smaller dia bolt? The heat from welding should help release the stub.