Hi Team...Need your thoughts on this one. 

Was on the moterway doing a 4th gear roll on pull and the engine made a massive BANG sound out the pipes and clunk clunk clunk....I still had power - but bugger all - so I switched her off and pulled over to the side of the road ASAP.

Specs are....86 EVO running a Turbo.

Any thoughts on this symptom?

Cheers

Does it run a carb or is it injected?

Could have blown the carb off the manfold during the roll on and that would be the bang. Was it pinging during your roll on?

She is a carbby system....The clunk clunk sounded more internal though.

I'll was thinking of starting with the cam chest first to see if i dropped a lifter and then a comp test to see how the jugs a looking.

How does that approch sound?

Sweet....Well there's my evening shot tonight!

I LOVE my missus though....driving home in the rental truck with the bike in the back she said i should get a spare Harley...a Roadking of all things!...

I am curious to see what went BANG though.

Serves me right for running 18lbs of boost!

Even luckier when ya got 2 bikes sittin in the shed.

FOUND IT! PaulyBronco was the closest. After loosening all the bolts I was about to rip the Cam Cover off and was thinking that there is no way the carb would blow off the bike, but lets have a gander anyway before I delve in too deep.

The Carb is still there BUT the top of the carb is nowhere to be seen!

The boost clean blew the entire top off the carb, leaving the four mounting screws firmly behind.

I have some pics that i will post up in a sec.

Whew!...that was a warning and I got off real lightly this time round.

Lucky boy! Sounds as though you have a serious boost spiking issue that results in what you are looking at now.

 Well here is what I suspect is the problem!...LOL (damn cheap plastic tops)

well i seen most stuff with the EVBT , but never seen that before, she would have  too  be set up proper for 18lbs' boost

f..k something new,

did you turn motor over?

like i'm deaf so would only feel a power loss, but you said it went Bang then clunk clunk internal, just wondering where the clunk clunk internal is?

 

That would explain the bang, but what about the clunk clunk?

I am thinking the clunk clunk may have been a chuff chuff as the air was pushed out the top of the carbby. However the one massive assumption I am making here is that it was the boost pressure that blew off the top. It could have been something else giving way and blowing back into the carb causing the top to lift off - unlikely but still a possibility.

I'm going to get a new top this morning and then do a compression test on both jugs just to be sure that the only broken bit is the carb top. I measured them about 2 weeks ago and they were at basically at 150PSI each - so I have a good baseline number to work from.

I'll know for sure by this afternoon.

good luck, hopefully that`s all that`s wrong, but to back fire like that i`d think something else caused it, compression test will tell you more.....

How did you go mate?

It's been over 40 degrees in the shed today so will wait till this evening. I got a new top and vacum slide so will do a comp test first and then put all the bits back together.

Ps: don't tell badcooky that I bought another turbo...

Yes....The current one seems to have a problem holding the boost back at 10lbs. It keeps going up to 18+lbs - (which is okay I suppose as the fuel system is built for 30lbs) and thats just way too much power for the stock engine setup - its got to be well in the 120-130Hp space at the moment.

I managed to score a referbished one on EBay and its in the mail! once its fitted i should be able to fix up the current one and either keep it as a spare or sell it on.

Hey Tussuck, are you sure your measureing the boost pressure right?

i know bugger all about hair dryers  but was told the one your useing has variable veins, is that right? i'm thinking you want to start to worry about your bottom end as those roller bearings can only take so much shock then they break up.

John Treese made a solution to that problem and the old Nitro motors use his bearings not sure if they will fit your EVO but you could ask. then if your lucky you could score a set of his cases and really start to turn it up.

good luck.

 

I spoke to John a few years back about options for my Evo heads....That man has forgotten more about performance engines than I'll EVER know - he is a guru.

The root cause of my grief is that my Aerocharger is no longer automatically limiting boost to 10lbs, for some reason it intermittently goes off the charts and boosts up to 18-20lbs. My boost gauge stops at 15 however I run a Zeitronix logger system with a damn high quality pressure sensor connected to the chamber that feeds to the carb and its telling me I’m hitting 18lbs.

18lbs is way too much for my engine setup (Its fine at 5-10lbs but no higher as that takes my power output into the 120+HP region, whcih is not a good place to be for a basically stock Evo engine) so currently it’s a matter of just keeping an eye on the boost gauge and backing off when its creeping over 10lbs.

I have another Aerocharger turbo on the way from the States to replace this one which will then allow me to inspect it for issues – I suspect it needs a refurbishment as the vairable vanes are most likely not closing properly, which means shipping it back to the USA for service; so I’ll cross that bridge when I get there.

I did mention a few days ago that you had that spiking problem........