Prop choice

[Ianfs]

It's great you had a good time with your children, my best memories with my Dad were when we were boating.

I'm a bit confused though.......................High 5, 21 or 19? and 4000 or 3750?

At present, i have a High 5 with 21P 48 16318 fitted. This shoots the boat up on the plane super quick but tops out at about 30 kts @ around 4000RPM.

[quote ]the results were a little confusing.. with the High five 19p i could achieve around 30 kts at max, @ around 3750rpm[/quote]

Is the High 5 a 21 or a 19P?

the Mirage Plus 19p gave an increase to about 35kts max but revs maxed out at 3000rpm.

Are you sure the Mirage is a 19P and is the High 5 a 21P or a 19p? With the results, the Mirage sounds like a 21p and the High 5 a 19P????

I'm not fussed at top speed at all but it seems odd, i am fully aware though that i do have a full tank of water and fuel too so top end will change with that but not revs??

Yes and no! I would say that if you were achieving 4,800 rpm with 1/4 tanks and 2 people and say 35knts, then you filled she would drop to say 4,500 rpm and say 32knts.

35knts is a reasonable speed for your boat, that's about 40 odd mph and with a misfire. I'm now thinking I would check the connections to the rev counter!

Oh and the Brass thing on the Distributor Cap with the 90 degree return is a vent.....

Distributor Vent.png (280.18 KiB) Viewed 13684 times

[Ianfs]

Oh and you have a Rochester Quadrajet, one of the best Carburettors ever made!!

You might want to think about a rebuild though, but we are talking of maybe 40-50quid for parts and a bit of a clean out. But I don't think this would cause a misfire.

If you get beyond the items I've mentioned, then Ed or a marine mechanic would be my next choice!

[_Ed_]

Locate the missfire with this:

http://www.ebay.co.uk/itm/Handheld-Non- ... 4853f51a71

The cylinder missing will be much cooler.

You should cruise back to a birth whilst its missing (not too much load) and also remove all the plugs to inspect. Look for the one/s that look different to the majority.

Missfires can be a few things and can cause serious engine damage so you must look into this sooner rather than later.

Ed

[_Ed_]

If the above btw doesn't show anything up (I'd be surprised) then you should also compression test the engine - actually you should do this anyway.

http://www.ebay.co.uk/itm/AUTOMOTIVE-PE ... 51b3a32b06

[shibbs]

Thanks so much for the input gents, i really do appreciate it.
My mistake on the prop Pitch, they are infact both 19P and i'm pretty sure in the past it would run up to 4000rpm, now on the mirage definitely only 3000rpm.
With regard to the rev counter, i am happy this is reading correctly as i gave it a 'blip' in neutral to see if it would pass 3000rpm and it did no problem so i think i can rule that out.
I will be able to get a temp gun at work so will give that a go. In the mean time i do intend to remove the plugs and check condition and spark and also do a compression test, hopefully this will give me something to work back from..
I think to be honest though, as you advise Ian, after these few basic checks i think due to my lack of knowledge on this engine i will probably get in touch with a mechanic on this one.
Anyone recommend a good marine mechanic in the hants area?

[_Ed_]

Unless you really dont want to do it yourself, do as I suggest and post results (and even pictures here).

Remember that when you do a compression test to take the kill chord out and you need to somehow do it with the throttle open. A closed throttle will give incorrect readings and usually turn it over for about 5 cycles per cylinder.

[Ianfs]

Thanks for posting Ed.

Shibbs, yes go with what Ed has suggested in the first instance especially wipping out the plugs and posting pictures, compression test and temp. Ed will be able to advise better than I and there may be a simple fix.

Also I forgot to say but you mentioned the STBD riser, so just to be sure we are on the same page, risers are small extensions lifting the exhaust elbows off the manifolds, some engines/boats have them, some don't. They are there to lift the elbows above the water line at rest where the boat stern sits low and although the flappers in the exhaust tubes will stop wash, at rest water would eventually seep in and into the manifolds if boat sits low, does this make sense? But as said you may not have them or require them as your elbows may sit comfortably above the water line.

I think you may therefore be referring to the Elbows and that the Starboard Elbow is very slightly hotter than the Port side? It's not uncommon when the exhausts haven't been changed for a while as there will be a build up of corrosion in the exit of the Elbow so water flow will be slower. It is a bit of a signpost though and although yours may not be leaking yet and may not leak for a while you ought to think about changing them out. Are you able to check its history at all to find out when they were last done?

[shibbs]

Update,
Ian, to clarify, yes you are right, i meant the exhaust Elbow, meant to take a picture earlier to confirm but yes, the STBD elbow. They were replaced approx 3 years ago and i do know the boat had very little use in that time. Will certainly plan to remove for inspection at the end of this season.
I went down today to carry out some checks on the plugs etc etc and found the following..
Although i was unable to get the tools i wanted from work , (a compression tester or temp gun) i did take all the plugs out one by one to inspect and test the spark strength .
I found that the spark on most of the cylinders did seem fairly week but there was no spark at all on cylinder No5. The engine even started and ran as normal without No5 HT lead connected, when i say normal, i mean normal as in how it has been running for some time(how i thought WAS correct until only recently). Clearly now i know this is not the case. Quite impressed how well it has done seeing as it seems it has only been running on 7 cylinders..
I checked the spark directly from the Coil and this proved to be very good and strong. does this mean the distributor is packing up or something else.
I assume that it has been running on 7, giving the lack of revs and now the spark seems to be deteriorating and has started the mis-fire on other cylinders under load?
I also turned the fuel off to see if any water was expelled from any of the cylinders whilst the plug was out and nothing (Phew, although it was obviously not under load) does this mean i can rule out the manifolds and possibly the carb from the equation do you think?
Thanks for your input so far gents!!
(I might change the name of the subject as clearly this has nothing to do with the prop )

[mlines]

Has the plug lead failed?

[shibbs]

Has the plug lead failed?

An obvious option - that i didn't even consider checking!
I think i had convinced myself that it was something to do with something further back as the rest of the sparks weren't great..
Will certainly swap out the lead and try another in its place though..
Thanks.