View Full Version : TZR help required

dazling - n/a
16-Apr-06, 10:34 PM
well i took my craft to have it the engine set up this week and was told there was a problem ! so i took the engine out and back to my engine guy , they have stripped it completely and rebuilt it and said it was ok . so i spent the afternoon putting it back into my craft started it up and im still getting the same problem http://hovercraft.org.uk/images/icons/smiley_icons/icon_mad.gif

the problem is , only one of the cylinders appears to be running correctly (one exhaust gets hot while the other stays cold ) so we swapped the coil leads over to make sure it wasn't a doggy coil and still no joy , next we swapped the carbs over to make sure it wasn't a carb problem and still no joy ! the engine revs well enough but i'm concerned ! everything i've tried has no effect on it at all , i have good compression etc and am now pulling my hair out ( what i have left that is )

has anyone else experienced this before ???

any help greatfully received as this is all thats stopping me using it now


Nick Long - n/a
16-Apr-06, 10:45 PM
This may or may not help, but it is at least some help for the diagnostic technique.

The TZR has a double spark system - both cylinders fire together at twice the required rate. So swapping the plug leads over doesn't change anything. You could in theory still have an ignition system firing on only one cylinder - its the timing that matters, not the connection of the leads.

And you could also have a bad sparking plug - try swapping the plugs over.

Is the power valve system working ok? The motor drives one cyclinder and there is a coupling to the other.


dazling - n/a
16-Apr-06, 11:29 PM
thanks nick , i've tried new plugs in both cylinders and nothing changes , the power valve aren't being used at present either and have been bolted so they dont move until i get the engine firing properly

i dont know how to check the ignition timing at the moment , sure i can find it somewhere , the guy thats been doing my engine is completely lost now too

thanks again


cozyhomer - n/a
17-Apr-06, 10:27 AM
Hi i am new to this hovercarft business.I just bought a rd 350 ypvs if you want i got some electrical testing diagrams so you can try if out email me on cozyhomer@hotmail.com hope it helps.

cozyhomer - n/a
17-Apr-06, 10:36 AM
Oh by the way you maybe able to help me out as well just building my craft at the moment so can you please email me as i dont want to post the questions on post in fear of ridicule thanks from brian.

Nick Long - n/a
17-Apr-06, 10:46 AM
Hi Daz,

Well let's check the big obvious things first. Can you do a compression test on each cylinder? That would show up problems with, rings, pistons, ports, reed valves ,etc.

You will get some idea turning it over slowly by hand - you should feel 4 small compressions per turn - but you really need a gauge that goes into the plug holes and a starting speed turn to do it properly.


andycollins - n/a
17-Apr-06, 04:09 PM
It's interesting that one side gets hot and the other stays cold. That seems to imply that one side isn't fireing at all and considering what you've already done, swapping carbs, new plugs etc. that's very odd.

Also odd the the revs are good. If one cylinder isn't firing it would etc like a dead weight and the engine wouldn't rev. e.g. when one of the throttle cables snapped on my craft and the slide closed completely, the engine wouldn't pull past 6-7000 RPM.

Could it be that both are fireing but one is way too lean and so is running far too hot? There will be two small connectors, one on each of the rubber that join the carbs to the reed valve cases. These are used to drop oil in when the engine is on the bike. As you'll be using pre-mix fuel/oil both of these should be blocked. If they aren't, the engine can draw air in after the carbs an it will run lean/hot.

It might be worth a check.



team black - n/a
17-Apr-06, 05:43 PM
1. The timing is fixed on a TZR, so that won't be wrong

2. the compressionis Ok on both barrels if both are greater than 100psi

3. Check your reed valves

4. Have you modified the exhaust in any way?

dazling - n/a
17-Apr-06, 06:56 PM
thanks for the help guys , lets see if i can address each one in turn tho

1, compression test has been done and showed just over 100psi on each cylinder

2, exhaust came with the craft when i bought it so i wouldn't know , but they both seem identical ( if that helps )

3,reed valves appear to be ok , i'll order new one just incase tho

just a thought tho now you mention it , i have just had the carbs rebuilt and new needle valves put in , but then again swapping the carbs over didn't solve the problem either

4,i can find the pipe that comes off the reed valve case and the pipe joins to the other reed valve case ( is this correct ? )

hope this info helps out

im just sooooo frustrated now cus i know its almost there !


Paul Fitz - n/a
17-Apr-06, 08:22 PM
Hello Daz,

If the engine has been totaly rebuilt I would check the following

1 Compression test - both cylinders should be equal. (pull the engine over three times on each cylinder to build the pressure)

2 Remove Carbs and check that *ALL* the jets are fitted. (Note the mainjet sizes and needle positions) Blow all galleries through.

3 Check that the needles are in the same position on each carb.

4 Check that the floats are working and adjusted correctly

5 Check that the fuel lines are clear.

6 Check the carb in-line filters are clear if fitted

7 Remove the Reed blocks and check the valves

8 Remove the exhausts and check that they are not blocked.

9 Check that both pistons are fitted the correct way round.

10 Check for any sign of fuel leaking at crankcase or gasket joints.

11 Check for potential air leaks on the inlet rubbers.

12 Check that the power valve seals have been fitted.

13 With the engine reasembled check that the throttle slides are balanced.

If the engine is not running on both (one exhast cold) a large quantity of fuel will collect in the crancase and exhaust unless little or no air is passing through the cylinder, this is usually evident when fuel drips from the exhaust connection. The plug will be wet. If this is not the case, it is more likely fuel starvation than electrical.

After checking the above make sure that both float bowls are full and start it. Run it at a fast idle. Pull the *non-working* plug-cap off to check if it *is* running or not. (gloves recommended :o/ ) If the engine runs unaltered, Insert a screwdriver into the plug-cap and check for a spark between the screwdriver and a handy earth (e.g. Cylinder head stud).

This should determine if everything is in order mechanically and determine if the problem is fuel or electrical.

dazling - n/a
18-Apr-06, 08:26 PM
hi ya paul , thanks for the info , i removed the exhaust today and found it blocked , i cleared it out and retried it ............its WORKS !

she hovered and almost fell off the trailer , i stopped it and took it off the trailer , ran it again and flew up the car park turned round and flew back again ! my first time in a hover .....im now very aware that you have no brakes and very little steering ! infact i ended up in the road ! ( its on an industrail estate so no traffic around luckily )

thanks again to all who helped out , just need to learn how to control it now ! ( in a field i think next time tho )

im sooooooooo happy now , my first time , i'll never forget it !!!!!!


cozyhomer - n/a
18-Apr-06, 08:37 PM
Well done daz i am very proud of you enjoy your test runs.Cant wait for my first run GOOD LUCK DAZ

dazling - n/a
18-Apr-06, 08:41 PM
cheers for that , must say tho its quite weird and going to take alot of getting use to ......still hoping to race it tho so alot of practice required


tonybroad - n/a
19-Apr-06, 08:21 AM
Good job

find a big field with nothing to hit - keep an eye on your plug colour to gauge how your new engine is performing - once it is warmed up hold it at max revs for a few seconds and cut the ingnition - the plugs should be a colour beteewn a rich tea biscuit and a bourbon


richardevans - n/a
19-Apr-06, 11:03 AM
Well done DAZ.

Don't forget that the big difference between a novice with a self-build and a novice with a bought craft is that the self builder will spend their first few races not just learning how to drive the thing but also working out what mods are required to make it reliable!

Richard E.

dazling - n/a
19-Apr-06, 03:09 PM
cheers for the encouragement guys , cant wait to go out again now , might just be able to tonight tho hopefully , failing that im def out tomorrow night no matter what !

DAZ http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

p.s , i feel like a dog with 2 #@*%$ , i cant stop thinking about it now or talking about it , i take it this is normal then .....vey addictive

richardevans - n/a
19-Apr-06, 04:10 PM
Indeed it is.

Just take pity on your (ex-)friends!