My bike came fitted with some very poorly designed stainless downpipes, 4 into 1, huge bore sizes throughout, no balace pipes anywhere, the bike had a bad flatspot between 5-7.5 k rpm, I reduced the pipe size after the collector to approx standard and this helped a lot, the flatspot is now between 5750 rpm and 7250 rpm , I've tried different needle positions and the carbs are spotless. Now for the bonkers bit !! I'm seriously considering reducing the downpipes sizes by squashing/crushing them down to approx the same cross sectional area as a standard pipe. I guess the crushed area will be about 7 inches from the head.
Any comments or advice would be great,
Old enough to know better
Sounds a bit drastic to me and I'd be surprised if it worked. If you could try some standard pipes, even if they are cosmetically challenged and needed some patching up, it would confirm if your existing pipes are really the problem. Might even be someone on here with a spare set after fitting stainless pipes and if your really lucky living not to far from you.
I would be of the same opinion, don't fix something that might not need to be fixed, best option is to get it to someone to dyno it, better put in the cost now rather than maybe having to pay for dyno anyway and then a new set of pipes aswel, that would be a right pain
And if you go to a decent dyno operator they will probably be able to re jet it and sort the problem.
(11-11-13, 06:31 PM)Fraser link Wrote: My bike came fitted with some very poorly designed stainless downpipes, 4 into 1, huge bore sizes throughout, no balace pipes anywhere, the bike had a bad flatspot between 5-7.5 k rpm, I reduced the pipe size after the collector to approx standard and this helped a lot, the flatspot is now between 5750 rpm and 7250 rpm , I've tried different needle positions and the carbs are spotless. Now for the bonkers bit !! I'm seriously considering reducing the downpipes sizes by squashing/crushing them down to approx the same cross sectional area as a standard pipe. I guess the crushed area will be about 7 inches from the head.
Any comments or advice would be great, ....if you do end up going down the road of reducing the headers"...see if you can find a machine shop and have some sleeved inserts made?...crushing/squashing just going to end up being a bodge!!....tbh..i think the balance pipe makes a huge diffrence  .....mabe a machine shop could sort that too?
You are not bonkers.
I recommend that:
You first put all the carb settings back to standard.
For my experience with stainless steel downpipes see below:
If you change your exhaust headers make sure the restrictor point of the new set is similar in overall opening size to the original set.
The original outlet measured: 35mm (narrowest point) to 43.5mm (widest point) externally at its most restricted point.
I’m not sure what the wall thickness is but I reckon it must be somewhere between 1.0mm and 2.00mm, my original pipes are still in good condition and I was loathe to saw them up to find out.
In any event the Motad replacement header system outlet pipe is has a clear open area of 1364sqm. Whereas the original outlet is restricted to somewhere between 962sqm and 1075sqm.
When I fitted the Motad headers the power band almost evaporated and a gas analyser showed it be running far too weak, this being supported by the plug colour, which was whiter than the bird that new seven dwarfs.
A further test was done by a lazer temp gauge on the exhaust clamp bracket of both original and new pipes and this showed the exhaust gas temp had risen.
To solve the issue the Motad pipe was sleeved down first to 1075sqm which improved things no end, and finally down to 975sqm, which seemed to be better.
Plugs were checked and exhaust gas analysed and the results were as good as I could get them.
My guess is you need to sleeve the outlet down to below 1000sqm. I used a bit of old heating pipe.
I have some spare pipe left over from when I did mine, so if you live near Bolton, you can borrow it and see if it works.
Or I can fit it for you (it's already pre-drilled to enable removal) and you can test by going up a hill near where I live.
Thanks for all your replies, I have already sleeved down pipe after the collector as you suggested Paul, I read your thread a few months ago and it has helped a lot and the carbs are back to std settings, but I don't think I will ever get the full mid range back without duplicating the original downpipe/collector design, I am happy to go out and buy another set of downpipes but its a lot of money if they don't make any improvement. An original genuine set in good condition would be great but I don't think I've got much chance of finding any. Maybe I will think on this for a while , and finding a local Dyno shop would also be a good idea.
Old enough to know better
More people are born because of alcohol than will ever die from it.
(12-11-13, 07:36 PM)darrsi link Wrote: http://www.yamahamotorcyclespares.co.uk/...aust?uID=0
Get a new set, they're a bargain :eek :rollin :rollin :rollin You had me looking in expectation there, I think I'll get the silencer as well!
12-11-13, 09:56 PM
(This post was last modified: 12-11-13, 09:57 PM by darrsi.)
(12-11-13, 09:36 PM)limax2 link Wrote: [quote author=darrsi link=topic=10678.msg112872#msg112872 date=1384281381]
http://www.yamahamotorcyclespares.co.uk/...aust?uID=0
Get a new set, they're a bargain :eek :rollin :rollin :rollin You had me looking in expectation there, I think I'll get the silencer as well!
[/quote]
May as well chuck in a wheel while you're splashing the cash 
http://www.yamahamotorcyclespares.co.uk/...heel?uID=0
More people are born because of alcohol than will ever die from it.
(12-11-13, 10:05 PM)ddtwelve link Wrote: love the tyre price :eek
Does make you wonder how they sell anything at all?
More people are born because of alcohol than will ever die from it.
Of course, the not-so-funny side of it is how it makes it so easy to write off your pride and joy, and how these prices push up insurance premiums... :rolleyes
(12-11-13, 11:12 PM)nick crisp link Wrote: Of course, the not-so-funny side of it is how it makes it so easy to write off your pride and joy, and how these prices push up insurance premiums... :rolleyes
Yeah i thought that, just the cost of one of those tyres would be more than enough to write a bike off, even though you could buy so much cheaper elsewhere.
More people are born because of alcohol than will ever die from it.
To Limax
I've got an original set that's never seen rain... or salt.
There is no corrosion on them.
If your interested give a ring:
Works landline: 01204 845382 (8.00 - 5.00)
Or send me an e-mail and I'll send you pictures: greenhalghco@btconnect.com
To Paul, my fault but a bit of a misunderstanding I'm afraid. I'm not after a set, but if you want to sell I'm sure there will be some on here keen for a good set. Thanks for the offer though.
No problemo
They've been sat in the garage for years, I've just never got round to doing anything about it.
I think I've got lazier as I've got older.
Something should be done about it....... but not today, perhaps next week.
I think you've probably changed your mind anyway, but don't try crushing the pipes. It will mess up the airflow, probably resulting in more restriction than you aiming for. You won't be able to reverse it and won't be able to sell the pipes on.
My advice would be buy a better set, and sell your current (undamaged) ones to offset the cost.
I haven't crushed them yet !! I think a dyno run might give more of an idea of whats going on.
Old enough to know better
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