Eh up guys,
Just wondering why going for 25:1 jet on early 40s isn't recommended? Is this to do with crank sealing? Got one here that looks like it should be fine but fades under use. The carb looks to have the 25:1 jet and wondered if this could be the culprit. Points and everything else checks ok. Motor head is showing as 1957 on all searches.
Also what prop could you guys recommend for this motor with a clutched box?
Thanks in advance, Hip.
Jetting on 40
Moderators: John@sos, RickUK, charlesp, Charles uk
Jetting on 40
Kaftan, grow my hair, I wanna be a hippy cos I really don't care.........
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Charles uk
- Posts: 4977
- Joined: Wed Feb 27, 2008 4:38 pm
- Location: Maidenhead Berks UK
Re: Jetting on 40
There is only one choice for props on that lower unit, 3 bladed weed free.
But if you struggle to spin that @ 4k ish, you will have to resort to trial & error.
But if you struggle to spin that @ 4k ish, you will have to resort to trial & error.
Make it idiot proof and someone will make a better idiot.
Re: Jetting on 40
When you say fades under use, is it bogged down or is it fading away while out of gear as well.
If it is fading away while it is out of gear, you need to start looking at the power head and carb.
more info required!
If it is fading away while it is out of gear, you need to start looking at the power head and carb.
more info required!
"THE KING OF BLING"!
Is it better to over think, than not think at all?
Is it better to over think, than not think at all?
Re: Jetting on 40
Charles is right the clutched lower requires the weed free prop. I had a similar problem a few years back with a engine that would not Rev in gear. It had a prop from a direct drive 40 plus that has a slower running gearbox.
40 plus direct drive has a slower running prop.
40 plus with a clutch has a faster running prop. If you fit a direct drive prop on a clutched gearbox the prop will be too coarse and the engine will not be able to rev.
40 plus direct drive has a slower running prop.
40 plus with a clutch has a faster running prop. If you fit a direct drive prop on a clutched gearbox the prop will be too coarse and the engine will not be able to rev.
Re: Jetting on 40
Around the late 1960s the bearing bushes were changed slightly which allows the 25:1 mix to be used from that point, with the correct jet.
Re: Jetting on 40
Many thanks guys, defo food for thought. It bogs down in drive and runs fairly free otherwise, although not quite as crisp as I would like. From what I can conclude it seems logical to change the prop and the jet to be on the safe side.
Has anyone ventured into the realms of crank seals for these beauties? I know from back in the biking days of strokers that crank seals had a major impact on performance if they were shot.
Has anyone got one of the aforementioned props up for grabs? Cash or bits exchange, if I have owt you need....
Hip
Has anyone ventured into the realms of crank seals for these beauties? I know from back in the biking days of strokers that crank seals had a major impact on performance if they were shot.
Has anyone got one of the aforementioned props up for grabs? Cash or bits exchange, if I have owt you need....
Hip
Kaftan, grow my hair, I wanna be a hippy cos I really don't care.........
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headdownarseup
- Posts: 2484
- Joined: Thu Apr 04, 2013 2:26 pm
- Location: bristol
Re: Jetting on 40
Another question
Why are you running a clutched gearbox on something THIS old?
What's the matter with the original DIRECT DRIVE box? (they're not that bad really) or is the original gearbox no longer fit for use hence the desire to swap to a modern box!
With a lot of the older pre 68 engines with the older design of crank bushes they seem a lot happier with an oilier fuel mix (bit more smokey but it's a seagull after all) but that extra oil also helps to seal any leaks and aids with crankcase compression. In my humble opinion there's no real gains to be had from running at 25:1 unless you happen to be a tree hugger and are sensitive to such things. I would stick with the original factory spec and use 10:1 fuel mix along with a direct drive box. If after some further testing you feel the motor lacks a certain something try altering the carb a little by screwing in the needle jet or better still refit the proper 10:1 needle (villiers carb). Very easy to do but will involve some very minor dismantling to the carb . Even a small adjustment like this can yield some quite big improvements in the overall running of your motor.
"Fading" or bogging could suggest the mixture is too weak or too rich. These villiers carbs are quite easy to get wrong when swapping out the needle jet. The manuals suggest that the fuel adjustment screw (located at the top of the throttle slide) should be set FLUSH with the top of the slide. This is the factory setting and is also a good starting point from where to make an adjustment. Screwing this screw in/down will lean the mixture. Screwing out/up will richen the mixture. Too rich and the motor will 4 stroke and probably struggle to rev. I think this could be your problem.
Go over the basics again with your engine. Ignition and fuel, and if you have access to the equipment carry out a compression check. Very roughly speaking you should expect to see in the region of 85+ psi on the compression. Any less than this could point to worn piston rings or worse still a badly scratched bore in the cylinder! If that's the case then a complete strip down is in order followed by a phone call to John for some replacement parts.
On the flip side to this, i have heard of 1 or 2 of these 40 series motors with very low compression indeed and are still running with no apparent ill effects.
Jon
Why are you running a clutched gearbox on something THIS old?
What's the matter with the original DIRECT DRIVE box? (they're not that bad really) or is the original gearbox no longer fit for use hence the desire to swap to a modern box!
With a lot of the older pre 68 engines with the older design of crank bushes they seem a lot happier with an oilier fuel mix (bit more smokey but it's a seagull after all) but that extra oil also helps to seal any leaks and aids with crankcase compression. In my humble opinion there's no real gains to be had from running at 25:1 unless you happen to be a tree hugger and are sensitive to such things. I would stick with the original factory spec and use 10:1 fuel mix along with a direct drive box. If after some further testing you feel the motor lacks a certain something try altering the carb a little by screwing in the needle jet or better still refit the proper 10:1 needle (villiers carb). Very easy to do but will involve some very minor dismantling to the carb . Even a small adjustment like this can yield some quite big improvements in the overall running of your motor.
"Fading" or bogging could suggest the mixture is too weak or too rich. These villiers carbs are quite easy to get wrong when swapping out the needle jet. The manuals suggest that the fuel adjustment screw (located at the top of the throttle slide) should be set FLUSH with the top of the slide. This is the factory setting and is also a good starting point from where to make an adjustment. Screwing this screw in/down will lean the mixture. Screwing out/up will richen the mixture. Too rich and the motor will 4 stroke and probably struggle to rev. I think this could be your problem.
Go over the basics again with your engine. Ignition and fuel, and if you have access to the equipment carry out a compression check. Very roughly speaking you should expect to see in the region of 85+ psi on the compression. Any less than this could point to worn piston rings or worse still a badly scratched bore in the cylinder! If that's the case then a complete strip down is in order followed by a phone call to John for some replacement parts.
On the flip side to this, i have heard of 1 or 2 of these 40 series motors with very low compression indeed and are still running with no apparent ill effects.
Jon
Re: Jetting on 40
Cheers Jon, great answer and gives me good reference. Think I got this motor almost as is although done a few precautionary/tidying bits to it.
Have not compression tested but judging from compression on pulling her over this isn't a problem. Had the block off to blast the clag from the water jacket and piston and rings are in great fettle. Points again check out fine. The screw on top of the needle is flush and after tweeking was where I was happiest with it. I left the box on it as the idea of a clutch appeals. I think it has a four or five blade prop on which may be part of the problem. I wasn't aware of different gearing on the fn box and indeed maybe a standard box could be the solution. I am sure that I have another carb on a good running 10:1 forty so just swapping should eliminate carb issues. If the 3 blade weed free prop suits this box has anyone hording one?
Many thanks.
Have not compression tested but judging from compression on pulling her over this isn't a problem. Had the block off to blast the clag from the water jacket and piston and rings are in great fettle. Points again check out fine. The screw on top of the needle is flush and after tweeking was where I was happiest with it. I left the box on it as the idea of a clutch appeals. I think it has a four or five blade prop on which may be part of the problem. I wasn't aware of different gearing on the fn box and indeed maybe a standard box could be the solution. I am sure that I have another carb on a good running 10:1 forty so just swapping should eliminate carb issues. If the 3 blade weed free prop suits this box has anyone hording one?
Many thanks.
Kaftan, grow my hair, I wanna be a hippy cos I really don't care.........