Spent nearly a year building this from many boxes of parts. Bought the best I could as I've gone along and after putting a few gentle road miles on it, I thought I'd get it set up on a dyno. 1st experience of a dyno and enjoyed every minute of the day we were there, until I saw the readout. 44bhp I feel absolutely gutted and it's really made me fall out of love with it. The dyno guy has said the pipes and barrels are a complete mismatch and as both are unknown, it's hard to know what to do.
Now, I realise I knew nothing about the motor except the barrels had been tuned (tampered with), so thought I'd just run and see (it had been sat at least 12 years). It runs lovely and with the new TM flat slides has a great spread of power but does just stop making anymore from about 9k I've borrowed a set of old Nikon pipes but I can't even find the enthusiasm to swap them to try. So give me some inspiration to sort the motor. I know I don't want (or can afford) a 421cc The barrels I've got are still standard bore but as I said unknown, the power valves are certainly not great and I've spent ages getting them to now at least open together at the same height. Do I go Athena and forget about power valves or should I get these barrels re-sleeved so at least I know I'm at base point. I see Yambits now have power valves back in stock but a sleeve and valves is probably knocking £500, that's a big chunk to go towards some "new" kit. Help
Couple of things, did he use an exhaust gas analyser and what ignition are you using
If the fuelling is way rich it won't rev or make decent power
Also if running a standard ignition it may need more ignition advance to get heat into the pipes
Also if your pipes are midrange and the barrels are tuned for top end it won't match up
Usually a tuned ypvs barrel is just inlets and transfers so shouldn't be too radical
Try the other pipes and see how it is
Yes, he did use a gas analyser, I was using 300 mains and we ended up at 350 after a few runs. I have a Zeeltronic, so we played with different curves for the power valves and he got different ignition curves stored so tried some of those too. He was saying (from experience) the way the power curve was it was the pipes that were wrong for the barrels but the problem was neither of use knew the tune on the barrels or what the pipes were made for. I just need to get my backside in gear and swap the pipes, at least I know the Nikons are top end pipes, trouble is that wasn't what I was after but I guess at least I'll know if they work or not. Thanks Mark.
Post by donkeychomp on Jul 25, 2021 21:43:46 GMT 1
Ah..a bit of lost mojo. Mate, I empathise. I did have 3 builds going at the same time a while back (now 2) and just sort of lost my way with them. Plus the fact there was so much other crap going on in my life...however I am now back on it and getting more enthused every day. Please don't give up on your bike, which is a cracker by the way. Maybe someone local can pop over to offer a bit of help to get it kick started again? (pun intended).
Take more than a couple of ink printed digits on a piece of paper for me to lose interest in summat that "runs lovely" Dont be daft and get on with it!
There are a few whose hobby is attaining numbers and graphs..... I prefer to ride them. A good bike isn't defined by a piece of paper alone, and big numbers aint worth a jot if it handles like a hunched pooing dog.
Before dynoing i trusted my seat of the pants dyno. It took me a year to setup my jetting to my spannies and empty airbox. When i went to the dyno i knew it was reliable and poky enough. 68rwhp with stock carbs. My advice is start rich and enjoy the process. You learn a lot of this on your own. 🤗
Be aware that a Dyno can say pretty much anything depending on what factors have been fed into it. 44 is also the figure at the rear wheel?
The pipes look like a lot like the Gibson hydroform units that I have (bought from this forum). Mine were said to be high end power pipes if that helps.
I would see if you can find someone locally with a standard ypvs 350 who will let you ride yours and theirs back to back, you might be surprised that yours isnt the dog the figures make it out to be. Of course you might also find that you need to make changes. Either way, it might be what enthuses you again...
Post up the dyno graph for us to have a look at. What size carbs are you running? Are they being used with a standard throttle cable? Your bike is very nice and I think you are lucky. It still seems to be a blank canvass with which you can do a lot with, using normal tune up accessories.
Bloody lovely looking bike. We’ve all been there, I lost my mojo on my last build a couple of times and the lads encouragement got me back on line and I’m so glad I did. Don’t lose sight of what you’ve done it really is a gorgeous looking bike. 👍
No one is born hating another person because of the color of his skin, or his background, or his religion. People must learn to hate, and if they can learn to hate, they can be taught to love, for love comes more naturally to the human heart than its opposite.
Probably all down to the pipes, I wouldn’t worry about the porting for now. Don’t exactly know who might have made those pipes but from the very early and aggressive downpipe section they look more like TZ350 pipes, Ie piston port pipes, rather than for a Reed valve motor.
I’d be inclined to get back on the dyno, use some standard pipes to get a reference curve and peak numbers and go from there.