GK73a Bandit 400 cylinder compression results

[moforockband]

Just curious if any other owners know what their compression results were. I'm thinking I need to rebuild mine, and check for bore/piston wear and valve seat leakage.
DRY on hot engine: 1-155psi, 2- 140, 3-140 4-140

WET on hot engine: 1-205 psi, 2-175, 3-155, 4-200

My bikes rides OK, but will not rev out, and is a real bitch to set up fuel wise. Bandit manual says 142-206 psi hot? What's real world figures with bikes with 20/30k miles under their belt?

[wullie3xv9]

Did a compression check on my GK76 spring this year. Figures recorded on a cold engine, but I did spin the engine with the starter for a few seconds with the plugs removed to get some oil on the bores beforehand, were between 10 & 11 Bar, which converts to 147 & 161.7 psi. No idea exactly how many miles my engine's done as it was a replacement fitted by the previous owner but it must be around 20 -30 thousand miles.

[moforockband]

Thanks for the info. The more I look into it that the compression is critical on these little 400's to ensure they run smoothly.
I think mine years back was 170 ish but it only had 8000km on it, but it's so long ago now!
Yours sounds OK, I take it, that it revs out nicely with your readings? Nick.

[wullie3xv9]

Apologies for slow response, been busy with work & rebuilding my 3XV's engine.
The carburation on mine still has to be fine tuned, but it rev's on past 12,000 rpm in 6th with 15/44 gearing fitted.
(I raised it from stock 14/44 final gearing). It'll rev to 13,000 - 13,500 where it feels like it starts to stutter.
I've got new sets of OEM needle's & O-5 needle jets to fit & it maybe needs a size or 2 bigger on the main jets.
(It currently has 117.5's fitted).
It needs "dyno'ed" to check the fuelling out properly but I haven't had time to take into the local DynaJet place yet !

(My 76 has a single, large K & N filter in the stock air box with the large intake ring fitted & also a set of Sandy Bike Spares stainless down pipes, R6 link pipe & an old, round Skorpion end can. I've also made & fitted a length of wire with an inline 1.5 K ohm resistor to fool the CDI into thinking the bike's in 3rd gear. Oh! And I've also slotted the ignition pickup/trigger's mounting plate holes (inside the L/H crank/sprag clutch cover) to advance the timing 3-4 degrees).

HTH.

Wullie.

[stripes1976]

Apologies for slow response, been busy with work & rebuilding my 3XV's engine.
The carburation on mine still has to be fine tuned, but it rev's on past 12,000 rpm in 6th with 15/44 gearing fitted.
(I raised it from stock 14/44 final gearing). It'll rev to 13,000 - 13,500 where it feels like it starts to stutter.
I've got new sets of OEM needle's & O-5 needle jets to fit & it maybe needs a size or 2 bigger on the main jets.
(It currently has 117.5's fitted).
It needs "dyno'ed" to check the fuelling out properly but I haven't had time to take into the local DynaJet place yet !

(My 76 has a single, large K & N filter in the stock air box with the large intake ring fitted & also a set of Sandy Bike Spares stainless down pipes, R6 link pipe & an old, round Skorpion end can. I've also made & fitted a length of wire with an inline 1.5 K ohm resistor to fool the CDI into thinking the bike's in 3rd gear. Oh! And I've also slotted the ignition pickup/trigger's mounting plate holes (inside the L/H crank/sprag clutch cover) to advance the timing 3-4 degrees).

HTH.

Wullie. [emoji2]

Have you changed your pilot jets with the k&n?

[wullie3xv9]

Quote Stripes1976 :- "Have you changed your pilot jets yet?"

When I first fitted the large, (single) K&N filter kit I replaced the stock 47.5's with 52's, but the fuelling around 3.5 thou was awful, the engine struggling to pull cleanly no matter how small or large the throttle input. It improved when I refitted the stock p.j's. but it's still not perfect. With the 47.5's fitted it gets worse as the engine warms up so it's still a bit rich, but that could be down to wear between the parallel portion of the needles & the needle jets, no ??
Or do you mean the much smaller (12.5 ??) pilot jets that are down a passage in the jet blocks??
If you mean them then no, I haven't changed them.

It really needs to be dyno'd to find out where in the rev range it's rich & lean so I can sort the carb's out once & for all. Between 4 & 13 thou I can't really fault it tho', as it pulls strong & clean, even with the bigger 15 tooth front sprocket fitted! I've read this a few times tho'.

http://www.factorypro.com/tech/tech_tun ... gines.html

[stripes1976]

I know the factory pro guidelines. In fact I have spoke in depth with from one of the guys there a long time ago trying to get needles and tubes made for the sp.
With all the bikes I setup with the k&n on the large port. It is required to increase the pilot jet. A rule of thumb it is generally for every 3 sizes on the main 1 on the pilot. There are a lot of possibilities. You have pm.

[wullie3xv9]

Thanks for the p.m., Stripes. At the moment the float heights are set at the stock 20 mm's.
In your experience, have they needed to be adjusted much ... if at all ??

Apologies for hi-jacking the thread, Moforockband !

[stripes1976]

I would say there is the possibility of it being on the rich side with the fuel height. Which could explain why it's not revving out.