1984 XS400 SECA Cafesque Build

[user11206]

Hello Everyone, long time no post, however I didn't want to post until I had a bike to actually contribute some information and pictures with. So my bike is a 1984 Yamaha XS400 Seca, my wife and in laws bought it for me for my birthday last year in 2015. Over the winter I had worked on it, and got it kind of wrapped up for now last summer so that I could ride. I have posted some pictures before, but I wanted to make an album and actual post everything I've done. So far this is what I have completed....

- Getting the bike back into a running and road worthy condition. This involved removing the carbs and putting them in an ultrasonic cleaning to clean them out, and replacing the
o-rings between carb bowls to stop the left bank from running leaner than the right. Built a simplistic carb balancer out of two beer bottles and some clear tubing. Balanced the carbs.
bike starts like a dream. Running the bike on 100LL aviation gas as I have an unlimited supply at work.
- Disassembling the bike, repainting the body paneling from purply pink to a British Racing green colour. Bondo existing Yamaha bracket screw mounts and sand. Need to get the tank repainted,
but it will do for the time being. Applied a carbon fiber decal as tank knee pads.
- Repainted the frame black. Repainted the forks black. Rebuilt and repainted the brake caliper. Disassembled rear fender and removed uneeded plastic, and glass blast and powder coat the
rear fender, grab handles for passengers, engine support mounts. Clean and polish rims, clean engine.
- Install clip on handlebars, changed the geometery of the headlight for the time being making custom aluminum brackets.
- Removed cable tachometer, built a plug for tachometer cable, and installed electronic tach.
- Installed two pod style chrome gauges. Reupholstered the seat with black leather.
- Changed indicator lighting system to a custom built LED panel, built top aluminum fascia for it (powder coated black and labelled).

Overall, happy with the way the bike has turned out so far. Definitely over the winter I am going to be focusing more on the engine. Pulling left and right engine and transmission covers
and will be painting them in crinkle finish paint. Replacing all hardware with hex head new stainless screws. Brighten up the engine with alumiprep.

Please check out pictures of the build and select to view from oldest to newest so you see the whole build in my tinypic account. http://tinypic.com/a/4js6t3/4
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[16VGTIDave]

Looking good! Nice to know there is yet another XS400 in the area, and a DOHC no less!. An unlimited supply of AvGas you say? Are you an AME? 100LL? You know that fuel has a higher octane rating than the engine needs, and much more lead than it was designed for. LL AvGas has 4x more lead in it than was ever used in AutoGas. Don't be surprised if you run into lead deposits and spark plug fouling issues.

With the engine side covers, expect to have to replace the paper gaskets when you pull them. The right side gasket in particular is complicated, and has pressurized engine oil run through it, so making one yourself isn't recommended.

Shoot me a PM if you'd like to grab a coffee some time, I'm often in Woodstock.
Dave

 

[drewpy]

avgas? you could always increase compression to make best use of it

 

[user11206]

Hey Dave, great to know that there are others in the area and I definitely will take you up on the coffee offer. My father in law and I (the FZR400 in the pictures you see) took a wicked ride down to Port Dover and a long the coast through Long Point - great summer ride.

Thanks for the tip on the side cover gaskets, I didn't know it was pressure fed through there so I will just order vs. making them out of cork.

As for the leaded AVgas, yes I am an AME at Waterloo International - Love how aircraft and bikes are similar lol. Yeah I know that the lead in 100LL is huge compared to leaded MOgas, I will be interested to see how the plugs fair, I might change to a finer wire Iridium or something to help combat that. Typically in an aircraft engine, we see that the lower set of plugs get fouled by lead as they are on the bottom and the heavy lead deposits will fall in. The tops for the most part don't get any lead, unless the aircraft is running really rich. So I am hopeful that gravity will play in my favour and stay out of the plugs and that the low pressure in the exhaust will help pull it out of the cylinder on the exhaust stroke... But that being said it could very likely get stuck under the valve seat and I will have a whole other issue to contend with.

So far so good, running really good on it. If you'd like a jug I'm sure I could get some for you because we just drain planes and we don't have a bowser to filter it so it can't go back in.

 

[user11206]

avgas? you could always increase compression to make best use of it

Suggesting maybe milling the head? Is the engine interference fit?

 

[16VGTIDave]

Considering that the pistons are domed with valve reliefs, it is a safe bet that it is an interference motor. There should be some room to play with though.

You could also try advancing the ignition timing some as well. That would require elongating the mounting holes for the pick up coils to allow for some rotation. Might make for difficult hot starts though. Can't say for certain as I haven't been down that road yet, nor have I found much info on performance tuning of the DOHC engine.

 

[user11206]

Yeah it could benefit from the spark advance, unfortunately its not an easy adjustment as you said the mounting holes would need to be elongated.

I want to play around with hooking up EGT probes on the exhausts and record the data of the EGTs and see what type of temps I am getting vs. RPM settings for the current jetting of the carbs. Since 100LL has such a resistance to detonation, I can use the EGTs as a indication when too much advance is too much, as the EGT will get extremely hot compared to a normal running condition.

I'm interested to try and tune the bike trying a different method of EGT measurement over the leaning schedule of the carbs instead of with an AFR alone. Considering the cylinder intakes are very similar the mass air flow of by cylinders are likely pretty close, aside from doing a proper port and polish and flowing the cylinders on a bench they won't get much better. But by finding the point at which one cylinder peaks on EGT vs Fuel Flow (while leaning) and seeing difference between the two cylinders I can lean or enrichen a carb to match the EGTs. Theoretically both cylinders should develop the same power.

On fuel injected aircraft (because its mechanically fuel injected) we match fuel flows to each individual cylinder because the intakes are fairly balanced, but as the volumetric efficiency of a cylinder starts to depreciate causing each to cylinder to flow less MAF so we will lean or enrichen an injector to compensate. This I wouldn't think would be much different because each cylinder is fed fuel separately.

All this might already be around, but I couldn't really find much documentation on the internet. Not for anything old anyways. Any thoughts?

 

[Wolfe_11B]

Man I miss the old days of flying and watching the EGT and manifold gauge, playing with the enrichment to get best cruise fuel usage I need to get rich so I can get flying again.

 

[16VGTIDave]

Thoughts. Yeah, a couple:
- The DOHC 400 is a high swirl combustion design engine - YICS (Yamaha Induction Control System).
- Large jets are not needed unless the exhaust has little back pressure and allows for over-scavenging the cylinder.
- The likelihood of detonation is also reduced because of the high turbulence in the cylinder.
- The stock airbox is less than optimum, hence the differential stock main jets.
- Adjusting the ignition timing is a bother, but not difficult to accomplish. Though we are stuck with the advance curve as it is, unless lots of $ are invested.
- Most pilots don't really know what to do with the mixture adjustment.
- P&W PT6 FTW!

 

[user11206]

Thanks for the input. I always forget about that YICS because the little emblems are missing and I can't find replacements!

The YICS ibtroduces more issues in the tuning because I don't know if they may be blocked. I was able to syn. The engine up (fairly decent) without blocking them so that to me is saying they may be clogged up. My too end is not great either.

I was looking at the airbox and thinking "How can we make this better" it seems like it is barely getting any air to that box. However I mnow with these Carbs that throwing on a set of velocity stacks or cone filters messes with the carb tuning and you need to file down the jet needle etc. Sounds like a pain in the ass.

I'm in no rush to do this stuff, I just really like to tinker with things. There is a lot of things I do want to change on the bike but I am trying to balance out the enjoyment factor too at the moment.

16VGTI you seem to be really mechanically adept and know about aircraft! Are you a mechanic of some sort? Or an AME, pilot, enthusiast of aircraft?

 

[16VGTIDave]

As I understand it, the YICS on the DOHC 400 is basically a chamber in the head connected to the intake port. It creates a high velocity flow through the intake valve and into the combustion chamber during every intake stroke. This promotes greater atomization of the fuel and a more consistent charge. As a result, less fuel and smaller jets are required.

I wouldn't want to try to modify the needles other than adjusting their height. There are plenty of different profile needles available if you find it necessary to change the mid RPM fuelling beyond what the height can do.

I've learned a thing or two about a few topics over the years. More relevant to your question: Canadore College AMT program, class of '98, Deans list. Left the industry before getting my ticket. Currently self employed as an Apple trainer and consultant.

 

[user11206]

I've learned a thing or two about a few topics over the years. More relevant to your question: Canadore College AMT program, class of '98, Deans list. Left the industry before getting my ticket. Currently self employed as an Apple trainer and consultant.

I think you made the right move, aircraft maintenance is a shit game lol.

Yeah that chamber appearently has little semi valve set up with these little bleed holes (from what I read online) and they can get clogged preventing the chamber from mixing that A/F mixture. I should check if mine are clogged up.