97cc Seagull

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headdownarseup
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Re: 97cc Seagull

Post by headdownarseup » Sat Jan 13, 2018 2:50 pm

:shock: but also 8) How cool is that. Another seagull "tweeker" in our midst.

Gareth, you really MUST get this out on the water again and test it, then let us know about some general performance figures. Speed across the water, the type of boat you're using, engine revs etc. oh and the type of carb this outfit breathes through and report back when you can. No rush.
This is the sort of diy engineering i have in mind with an old 102 gull engine. (join in if you like in another section under "modified 102") Nothing too mad or extravagant, but still roughly within most people's grasp (and pockets) if they're willing to pay attention to all those small details. :P

I like what you've done so far, quite a lot actually.
I've tinkered a little bit with similar ideas on some of my own seagulls, perhaps not to the same extreme but still with some quite good results.

This is the kind of work we need to see plenty more of on this forum. Massive thumbs up from me fella :P
Love it


Jon

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NaughtyBits
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Re: 97cc Seagull

Post by NaughtyBits » Sat Jan 13, 2018 3:00 pm

Ha - for us this side of the pond, they're cheaper to get in your hand than a new BS bushing crank & con rod. Was just picking up on Charles' mention of the BS kingfisher needle roller crank - which haven't been available for sale for years from BS - that's all.

Really like seeing what you've done, GarethJ. Did you say you've managed to get it out for some testing? Any idea of how much you were able to increase the RPM's?

Have a good one.

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Charles uk
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Re: 97cc Seagull

Post by Charles uk » Sat Jan 13, 2018 4:26 pm

Ask your questions by email next time as none of the racers will give their secrets away in public, racers show off on the race course by results, not on the net.

Bermudians like Mr Bits, also known as Leonardo da Dremel is a very serious racer, who builds many types of very quick Seagulls, that I would steal given half a chance!
Make it idiot proof and someone will make a better idiot.

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NaughtyBits
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Re: 97cc Seagull

Post by NaughtyBits » Sat Jan 13, 2018 4:43 pm

Ha. I do love my dremel and $5 box of bits - that's true...! (And I've just been lucky to have a few extremely knowledgeable mates who haven't gotten bored of my many stupid questions yet... 8) )

Always good to see how other enthusiasts go about solving the same problems. Fun stuff...

headdownarseup
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Re: 97cc Seagull

Post by headdownarseup » Sat Jan 13, 2018 8:18 pm

Oooohhh touched a nerve there i think


Jason has a set of skills that has proven him some success as do you Chas. He obviously has a lot of patient mates on hand to help as well :P
Absolutely nothing wrong with that in my book Chas. but if we can't compare notes once in a while what's the point in having a section on SOS strictly for racing seagulls and racing in general!
It's a bit of harmless fun after all. It's not all about the winning or being the fastest. Omit what you like so as not to reveal all, but enough to keep others guessing.

Lighten up Charles, your time will come again if being the big cheese is what matters to you the most. It certainly wouldn't to me as i have far more important things in my life to worry about


ps
i also like my dremel but i'm no racer 8)

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NaughtyBits
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Re: 97cc Seagull

Post by NaughtyBits » Sat Jan 13, 2018 8:39 pm

? What are you on about?

You’ve obviously completely misunderstood Charles. I can guarantee you there’s no nerve touched there - especially with him being one of the few I try to bore to tears from time to time...
Last edited by NaughtyBits on Sun Jan 14, 2018 5:19 pm, edited 1 time in total.

GarethJ
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Re: 97cc Seagull

Post by GarethJ » Sat Jan 13, 2018 8:50 pm

Thanks for the positive comments!

Don't hold back asking questions to me, if I know the answer, I'll be happy to divulge.

My test (well, only) vessel is a 17ft canadian canoe. Not a racing boat (hull speed and that) for sure but quite fun.

Developments are as follows.
-standard, good silver seagull with barge pusher gearbox and an adapted (huge) weedless prop about 6knots (note, this is an entirely different motor but it says something about the canoe) the prop happened to be a real nice match for boat/motor
-The setup described on this thread but with a lower compression head and slightly thinner base gasket and probably some other alterations, with a 2.5:1 gearbox and an different prop (maybe mariner ~5-6hp) a bit faster than before but rarely see 7knots. Only revs to 3200ish on the pond.
-the setup above but with a higher comp head and a baby 2hp prop revved to more than the audible rpm gauge on my phone could handle. Replacement induction tachometer just arrived. Not tried on the canoe. I feel that a prop in between the two would suit better but will decide when I see what it spins this one at.

Have a choice of 3 carbs, a standard seagull amal, an amal from a BSA bantam (125) and a modern 50-80cc cheapy that was lying around. The modern one is a bit restrictive and top end is better with either of the others which is a real shame as it starts and behaves really nicely otherwise. The bantam carb produces maybe ever so slightly more rpm at the top end but is harder to start and not the nice mid/low rpm. I'm back on the seagull carb for now it's a good all rounder.

I've done some work to the ports, for better or worse! I tried to approach this on the basis of calculation but the cross flow situation and limitations of the design lead to some guesswork. Even if I had the details to hand, the non standard stroke and rod length would make the details pretty pointless if comparing to a standard 'gull.

I ought to try to find out the weight of a honda lead piston and calculate what I expect a sensible safe max rpm is based on the heavier seagull one.

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NaughtyBits
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Re: 97cc Seagull

Post by NaughtyBits » Sun Jan 14, 2018 5:58 pm

Good stuff, GarethJ. The faster Silver Centuries here have had good luck with the standard 400 series Amal carbs.

Re: the 2.5:1 gear box - are you working with one from the 102 or the clutched Century? There have been a few posts in the past on this that you might have seen already - but have you thought about using the 2.1:1 featherweight gearbox? That's another thing people have had good luck with here in the modified class.

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Charles uk
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Re: 97cc Seagull

Post by Charles uk » Sun Jan 14, 2018 6:32 pm

What's your Canadian canoe? Old Town, Coleman or GRP.

Mr. Bits is right on the money, with the lower units, I'd go for a 2.1:1 featherweight, & the carb is an Amal 416 (16mm throat) with a 95 jet.

I had a Coleman for several years that my son & I did a lot of miles in, with an EFPC sidemount, they just weren't meant to go fast & struggled in the sea.
Make it idiot proof and someone will make a better idiot.

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Re: 97cc Seagull

Post by GarethJ » Sun Jan 14, 2018 7:27 pm

Its an old town camper and isn't actually mine but it's all I have access to at the minute. It's a nice canoe and doesn't deserve to be treated as harshly as we have but my goodness is it tough!

Ah, right, I can see that a quicker 'box would have advantages, I wasn't actually aware there was a 2.1:1. I'll see if one of the seagull breakers can sort me out. Makes particular sense now I have a prop that I think is a bit small. I've no idea what the 2.5:1 is from, it is clutched and has a metal water pump with external water outlet which I quite like.

Re. The carb, my barrel has actually been opened out to I think 18mm. (Not ideal when using the 16mm!) It suits the bantam carb. So I'm tempted to try to test something else 18mm one day.

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NaughtyBits
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Re: 97cc Seagull

Post by NaughtyBits » Sun Jan 14, 2018 7:49 pm

Charles may know which off the top of his head, but BS did use the Amal 418 on a model or two. They do pop up from time to time (though not as frequently as the 416 & 420) and would probably work perfectly for you, GarethJ.

Or you could open the 416 out to match?

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Re: 97cc Seagull

Post by GarethJ » Sun Jan 14, 2018 8:07 pm

I have been tempted to doctor the 416 but it's my only one and I'd like to keep enough bits to rebuild the silver in original state if I can. Plus something doesn't quite feel right to go boring out the fuel metering device that relies on Venturi to work properly. I'm sure an 18mm carb will find it's way to me one day to try.

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Charles uk
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Re: 97cc Seagull

Post by Charles uk » Sun Jan 14, 2018 8:30 pm

What's the ID of the inlet stubb?

Curlews were the only Seagull that used the Amal 418 with a 100 jet.
Make it idiot proof and someone will make a better idiot.

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NaughtyBits
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Re: 97cc Seagull

Post by NaughtyBits » Sun Jan 14, 2018 8:35 pm

18mm, Charles. Doesn't one of the 416 series & the 418 appear to share the same body? I'll poke around my carbs later tonight and check...
Last edited by NaughtyBits on Sun Jan 14, 2018 10:16 pm, edited 1 time in total.

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Charles uk
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Re: 97cc Seagull

Post by Charles uk » Sun Jan 14, 2018 9:40 pm

All of the 400 series have the same body, but with minor differences to the needles & floats, I've only taken a 416 out to 17 mm, I've just had a look at a 416 & should be possible, but I've never taken one that far, so don't bet your life on it!

Remove the emulsion tube with an aluminium drift with a center spigot.
Make it idiot proof and someone will make a better idiot.

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